Journal Archive

Johnson Matthey Technol. Rev., 2023, 67, (3), 303
doi: 10.1595/205651323X16691084445762

Additive Manufacturing of Platinum Alloys

Practical aspects during laser powder bed fusion of jewellery items

  • Ulrich E. Klotz*, Frank R. König
  • Research Institute for Precious Metals and Metals Chemistry (fem), Katharinenstrasse 17, 73525 Schwäbisch Gmünd, Germany
  • *Email:
    Received 25th July 2022; Revised 7th November 2022; Accepted 21st November 2022; Online 22nd November 2022

Article Synopsis

Additive manufacturing of jewellery alloys has been actively investigated for the past 10 years. Limited studies have been conducted on gold and platinum jewellery alloys. Platinum is of increased interest due to the technological challenges in investment casting. In the present paper, typical platinum jewellery alloys have been tested by laser track experiments on sheet materials. The effect of alloy composition on width and depth of the laser tracks was studied by metallography. Optimum parameters of the laser powder bed fusion (PBF-LB) process were determined for a typical 950Pt jewellery alloy by the preparation of dedicated test samples. Densities of >99.8% were reached for a wide range of processing parameters. However, for real jewellery parts the resulting density was found to depend significantly on the part geometry and on the chosen support structure. The supports must take into account the geometrical orientation of the part relative to the laser build direction and the orientation on the build plate. Local overheating gives rise to porosity in these areas. Therefore, the supports play an important role in thermal management and must be optimised for each part. The design of suitable supports was successfully demonstrated for a typical jewellery ring sample.

1. Introduction

Many different additive manufacturing processes exist for metals, polymers and ceramic materials. The present paper focuses on PBF-LB technology, the most widely used process for additive manufacturing of metallic alloys. The process is also known under different brand names using the same technology, such as selective laser melting (SLM) or direct metal laser sintering (DMLS). The PBF-LB of platinum alloy jewellery items has gained increasing interest in recent years. Pioneering work on the additive manufacturing of precious metals was done by Zito et al. (18). So far, most studies have focused on gold alloys (912). The effect of PBF-LB process parameters on 18 karat yellow gold was studied by Klotz et al. (9). Surface treatment of the powder allowed a reduction in porosity from 3% or 4% before treatment to below 1% after surface treatment. The addition of alloying elements, especially germanium, resulted in a reduction of porosity to 0.3%. At the same time, the surface roughness was reduced significantly.

Finishing and polishing of complex shaped jewellery is a crucial production step. Fletcher et al. (11) compared polishing techniques of LBPF produced jewellery items. Automated techniques are not sufficient to achieve the desired lustre and manual polishing remains necessary. A more fundamental work by Ghasemi-Tabasi et al. (12) describes a method to find optimum PBF-LB parameters using a so-called translation rule. The concept of normalised enthalpy is used to take into account the differences in thermal and optical properties among the different materials. Pogliani and Albertin (13) presented a case study for the production of a small series of jewellery by PBF-LB technology. They provide problem-solving insights into the technology in production.

Only a few publications present results on PBF-LB of platinum alloys (3, 4, 6, 14, 15). The first studies with platinum alloys were done by Zito et al. in 2014 (3). Platinum was found to be easier to work than gold due to its lower thermal conductivity. The addition of silicon and germanium further improved the surface quality and reduced porosity. A continuation of the work in 2015 (4) focused on the dimensional accuracy and mechanical properties of PBF-LB parts compared to cast parts. Flat products in platinum alloys can be produced with higher detail than curved objects, which is opposite to the observations in investment casting. Gold alloys allowed higher surface quality and better dimensional accuracy than platinum alloys. The geometry of the part (pave setting vs. ring) influenced the dimensional accuracy compared to the computer aided design (CAD) model. Again the work was conducted with non-standard alloy compositions that included 0.2–0.4% silicon and germanium (7).

The most comprehensive study on platinum alloys so far was published in 2018 (6). It provides a 1:1 comparison of the properties of several different jewellery items produced by PBF-LB or investment casting. The case study not only compares the technical aspects of the processes but also the production cost, production time and carbon dioxide footprint of both technologies. The investment casting process of platinum alloys is rather challenging and struggles with casting defects such as shrinkage porosity, microporosity or investment reactions (1618). On the other hand, the physical properties of platinum alloys, particularly the reflectivity of infrared laser light, are more similar to steel or titanium alloys (19). This makes the PBF-LB process of platinum alloys much easier compared to gold or silver alloys. The authors (6) conclude that platinum PBF-LB parts show higher surface quality, less porosity and therefore less repair effort during finishing compared to their counterparts produced by investment casting. The commercial benefits of PBF-LB are slightly shorter production times, lower production cost and lower environmental impact. The advantages of PBF-LB are particularly noticeable with production quantities of 500 g platinum alloy per week.

Laag and Heinrich (15) studied the powder manufacturing of different platinum alloys by gas atomisation in the Nanoval process. They provide mechanical properties and surface roughness data of parts produced by PBF-LB and PBF-LB plus hot isostatic pressing (HIP) in comparison to parts produced by metal injection moulding (MIM). PBF-LB results in higher density and smaller grain size than MIM, but these results were achieved for different alloys.

The present work is divided into two parts. The first part deals with the study of laser tracks on alloyed metal sheet in order to study the laser to alloy interaction. The alloy compositions include many commercial 950Pt alloys but also alloys of lower platinum content. The effect of alloy composition and the role of alloying elements on the melting behaviour was studied systematically by determining the width and depth of the laser tracks. This is the most comprehensive study so far on the role of platinum alloy compositions in PBF-LB processing. In the second part of this work PBF-LB trials were conducted with a commercially available 950Pt-In-Au-Ir alloy powder (alloy 951Pt P1, C.HAFNER GmbH + Co KG, Germany). The PBF-LB process parameters were optimised for minimum porosity. The effect of support structures was studied and effects on alloy chemistry and defects are described in detail.

2. Experimental

2.1 Laser Tracks on Metal Sheet Samples

A Concept Laser MLab R machine (GE Additive, USA) with a maximum laser power of 100 W was used in this study. The laser power was set to 95 W and kept constant for all tests. Despite the relatively low laser power a sufficient energy density could be achieved because of the small spot size (30 μm) of the machine.

Metal sheets of commercially available platinum alloys were obtained from C.HAFNER, Agosi AG, Germany and WIELAND Edelmetalle GmbH, Germany. Alloys that were not commercially available were prepared by induction melting from pure elements, except for ruthenium that was alloyed via a platinum-ruthenium master alloy. Precious metals were obtained from C.HAFNER. Additional alloying elements were provided by HMW Hauner GmbH & Co KG, Germany. All pure elements were used in a purity of at least 99.99%. Samples of approximately 40 g were melted in a centrifugal casting machine (TCE10, Topcast Srl, Italy) after evacuation to approximately 10–2 mbar and backfilling with argon to about 300 mbar. The composition of all alloys is given in Table I. Some of the alloys were obtained as commercial alloys and used without further modification. The origin and manufacturing of each alloy is described in the column “Remarks”.

Table I

Composition of Sheet Material for Laser Track Tests

Alloy Platinum, mass% Alloying elements, mass% Remarks
Pt-Ru bal. Ru: 1 / 3 / 5 Pt-5Ru from C.HAFNER, diluted with platinum to 1% and 3% Ru, respectively
Pt-Co bal. Co: 1 / 3 / 5 Pt-5Co from C.HAFNER, diluted with platinum to 1% and 3% Co, respectively
Pt-Cu bal. Cu: 4 / 4.7 / 20 / 40 / 60 / 80 Pt-4Cu and Pt-4.7Cu from Agosi and C.HAFNER, respectively. Alloys of higher Cu content prepared from pure elements
Pt-Pd bal. Pd: 20 / 40 / 60 / 80 Alloys prepared from pure elements
Pt-Ir bal. Ir: 10 / 20 Alloys from C.HAFNER
Pt-W bal. W: 5 Alloy from WIELAND Edelmetalle
Pt-Cu-Pd 60 Cu: 10 / 20 / 30, Pd: bal. Alloys prepared from pure elements
Pt-Cu-Ga 95.5 Cu:1.9, Ga: 2.7 Alloy from C.HAFNER
Pt-Cu-Pd 60 Pd: 10, Cu: bal. Alloy from WIELAND Edelmetalle
Pt-Ru-X 95 Au: 1.5 / 3.5, Ru: bal.; Co: 1.5 / 3.5, Ru: bal.; Cu: 1.5 / 3.5, Ru: bal. Alloys prepared pure elements and Pt-5Ru master alloy from C.HAFNER
Pt-Ru-Cu-X 95 Cu: 2.0, Ru: 1.0, X: 2.0; X = Ga, In, Sn, Ge, Zn Alloys prepared from pure elements and Pt-5Ru master alloy from C.HAFNER
Pt-In-Au-Ru 95.2 In: 2.5, Au: 1.5, Ru: 1.0 Alloy from C.HAFNER
Pt-In-Au-Ir 95.1 In: 2.7, Au: 2.0, Ir: 0.2 Alloy from C.HAFNER

Immediately after melting the alloy samples were cast into a copper mould of approximately 4 mm × 12 mm × 40 mm. The cast ingots were cold rolled with polished rolling mill to a thickness of approximately 1 mm. The sample surface was used in the as-rolled condition to apply the laser tracks. The laser tracks on metal sheets were produced in the Concept Laser Mlab R machine at a laser power of 95 W with a laser speed between 25 mm s–1 and 500 mm s–1. A set of laser tracks with a length of 5 mm was produced on each metal sheet (Figure 1). Each set of laser tracks was repeated three times. The width of the lines was measured by optical microscopy and averaged over the length of all three lines of the same speed. The depth of the tracks was measured in metallographic cross-sections in a scanning electron microscope (SEM). Samples for SEM were produced by standard metallographic techniques as described in Section 2.3.

Fig. 1.

Effect of laser speed on the line width and depth for 950PtInAuRu

2.2 Laser Powder Bed Fusion Experiments

Concerning the PBF-LB trials with alloyed powder, a two-step scanning routine was applied where the contour scan was made prior to the hatch scan. This was found to be beneficial for gold alloys in terms of reducing the surface roughness (9). The contour scan speed was 600 mm s–1 for all tests. The hatch scan parameters were varied to find optimum parameters with minimum porosity in a test part. The hatch distance and the laser speed were changed from 27 μm to 63 μm and 100 mm s–1 to 600 mm s–1, respectively. The powder was provided as alloyed powder. It had a size distribution of 10–45 μm (d10/d90 value) and was applied with a rubber lip wiper in layers of 20 μm.

The test part for the PBF-LB trials has an angular shape with wires and plates of different diameters similar to the one described in (9). The support structure and the slicing of the model was done with the software AutoFab. The part was oriented in a 45° angle relative to the movement of the recoater. After optimisation of the process parameters, jewellery parts were produced with these optimum parameters. An optimisation of the support structures was found to be necessary for some parts depending on their geometry.

2.3 Microstructure Investigation and Porosity Measurement

The test parts (metal sheets samples and PBF-LB parts) were embedded in epoxy (Epofix) and metallographically prepared. Grinding was done with grit P320, P600 and P1200 paper followed by subsequent polishing with 9 μm and 3 μm diamond paste. The last polishing step was done with 0.04 μm oxide polishing suspension. SEM images were obtained by a GeminiSEM 300 instrument (ZEISS, Germany) equipped with an energy dispersive X-ray (EDX) detector X-Max 150 (Oxford Instruments plc, UK) for local chemical analysis.

The porosity measurement was conducted by image analysis with the software AxioVision (ZEISS) on a stitched light optical image recorded at 5× objective lens (Figure 2). The horizontal part of the test sample was selected as region of interest (ROI). In order to determine the porosity the image was binarised using a threshold value at the minimum of the histogram. The porosity value is given as the percentage of black pixels inside the ROI.

Fig. 2.

Typical metallographic section of the test samples: (a) hatch distance 27 μm, laser speed 600 mm s–1; (b) hatch distance 63 μm, laser speed 500 mm s–1

3. Results

3.1 Laser Tracks on Metal Sheets

The laser tracks were made to identify the effect of alloy composition on the laser-material interaction. The simplicity of the materials production and testing procedure allowed testing of many different alloys as opposed to tests with powder. At constant laser power the width of the laser tracks decreases with increasing laser speed, because the energy input per length unit becomes smaller (Figure 1). The data points indicate the mean value from five individual measurements on each of three lines. The maximum and minimum width is represented by the error bars. The inserted SEM image shows a typical laser track in cross-section. The cold rolled microstructure of the metal sheet allowed a clear identification of the melting zone and of the heat-affected zone. The depth was measured as the distance from the averaged metal sheet surface to the maximum depth of the laser track. The depth is generally more prone to changes than the width because there might be a change from the conduction mode to the keyhole mode, which mainly affects the depth but hardly the width (please see Section 4.1 for an explanation of conduction and keyhole mode).

The effect of alloy composition was studied for binary platinum-palladium and platinum-copper alloys with a platinum content from 100% to 20% (Figure 3) at a laser speed of 100 mm s–1. The addition of palladium and copper shows a different effect on width and depth of the laser tracks. Palladium tends to lower both values in an intermediate concentration range of 40–60%. Especially the depth shows a pronounced minimum. (Figure 3(b)) shows the very flat laser track, which is a typical example for the so-called conduction mode. For higher palladium contents the depth increases again. Tests at a laser speed of 200 mm s–1 showed similar results. The addition of copper shows the opposite trend to increase melt pool width and depth, especially in the intermediate concentration range (Figure 3(c)). However, the trends are affected by scatter of the experimental data.

Fig. 3.

(a) Effect of alloy composition on track width and depth in binary platinum-palladium and platinum-copper alloys; the micrographs for: (b) Pt-60Pd and (c) Pt-60Cu show typical examples for conduction mode and transition mode, respectively

A series of ternary alloys with 60% platinum was studied in the platinum-palladium-copper system (Figure 4). If palladium is exchanged by copper, both width and depth increase which results in a change from conduction mode (Figure 4(b)) to keyhole mode. With 270–290 μm the depth is maximum for 20–30% copper (Figure 4(c)) where a typical keyhole mode occurs. For the binary platinum-copper alloy, the depth significantly decreases again to about 100 μm.

Fig. 4.

(a) Effect of alloy composition on track width and depth in ternary platinum-palladium-copper alloys with a platinum content of 60%; SEM images of metallographic cross-sections of the alloys: (b) 60Pt-30Pd-10Cu and (c) 60Pt-10Pd-30Cu

The effect of cobalt, ruthenium, copper and gold is shown in Figure 5. These elements were added in smaller amounts according to the compositions of typical alloys used in the jewellery and watch industry. No significant effect of these alloying additions on the width and the depth of the laser tracks was found. The values are very similar to pure platinum. A similar result was obtained for alloys with 95% platinum. Figure 5 shows compositions based on 95Pt-Ru where ruthenium is gradually replaced by gold, copper or cobalt. The width and depth are not much affected by such changes of the chemical composition.

Fig. 5.

Effect of alloy composition on track width and depth in platinum-X alloys of high platinum content

The addition of further elements was studied with alloys based on 95Pt-1.5Cu-3.5Ru. Ruthenium was partly replaced by 2% gallium, indium, tin, germanium or zinc (Figure 6). According to the binary phase diagrams, these elements strongly decrease the liquidus temperature and increase the melting range. The effect in the laser track experiments shows strong differences. The addition of indium and zinc has no significant effect, neither on track width nor track depth. Gallium and tin have an intermediate to strong effect, while germanium has the strongest effect. The track depth increases by a factor of six due to the addition of 2% germanium as shown in Figure 6(b). The alloy with the addition of gallium was prone to hot cracking (Figure 6(c)), which was not the case for the addition of other alloying elements.

Fig. 6.

(a) Effect of the addition of solidus supressing elements in ternary 95Pt-1.5Cu-3.5Ru-X alloys; (b) effect of germanium; (c) effect of gallium. X stands for gallium, indium, tin, germanium or zinc that replace ruthenium in the alloy

3.2 Process Parameter Optimisation in Laser Powder Bed Fusion

One of the objectives of the laser track tests was to obtain a first impression of the effect of the laser speed on the PBF-LB process. The results for the commercial alloys are shown in Figure 7. The error bars show the mean absolute deviation (MAD) of the average width. Taking into account the MAD most alloys show a width of 100–150 μm. The 950Pt‐W alloys are closer to 150 μm. Alloys with similar composition obtained from two manufacturers are marked by #1 and #2. However, the results show significant scatter. The depth values show a larger variation than the width values. By far the highest width and depth were obtained for 950Pt-Ga-Cu. This alloy showed the smallest MAD of all alloys tested.

Fig. 7.

Evaluation of laser track width and depth of technical alloys at a laser speed of 100 mm s–1. Some alloy sheets were obtained from different manufacturers as indicated by the hash sign

PBF-LB experiments on the alloy 950Pt‐Au‐In‐Ru were conducted with alloyed powder, since it is commercially available as powder. It was provided by C.HAFNER. Figure 2 shows two test samples produced by different sets of laser parameters. The part shown in Figure 2(b) was built with the optimum process parameters resulting in minimum porosity.

Generally, the porosity of this 950Pt alloy was very small (Figure 8) compared to other precious metal alloys (10, 19). For all hatch distances and laser speeds up to 500 mm s–1 the porosity was below 0.4%. The porosity increases with increasing laser speed and decreasing hatch distance. At 600 mm s–1 a significant increase is observed for most hatch distances.

Fig. 8.

(a) Effect of laser speed; and (b) effect of hatch distance. Laser power 95 W

The lowest porosity of below 0.1% (99.9% density) was achieved for a hatch distance of 63 μm. At this hatch distance, the porosity levels are nearly independent of the laser speed. For all hatch distances and laser speeds up to 500 mm s–1 the porosity was below 0.4%. The porosity increases with decreasing hatch distance and increasing laser speed. Decreasing hatch distance and increasing laser speed result in gas pores and lack-of-fusion porosity, respectively. At 600 mm s–1 a significant increase is observed and the process tends to become unstable. A hatch distance of 63 μm and a laser speed of 500 mm s–1 were identified as optimum parameters throughout this study. These parameters provided the lowest porosity at a very high process speed (high hatch distance and laser speed).

3.3 Design of Support Structures for Jewellery Parts

Two jewellery designs, typical engagement rings with three or seven stones, were provided by project partners for additive manufacturing. The rings were supported by columnar hollow supports in areas with an inclination less than 45° to the build plate (Figure 9). The supports were positioned symmetrically on both sides of the ring. The recoater applied the powder on the build plate perpendicular to the plane of the ring shank. The laser direction was from right to left. Defects occurred on the right side in unsupported areas of the ring shank. Over a certain length of the ring shank, material is missing, but only on the right, outer side of the ring shank. The problem starts at the end of the support structure and it ends at a build angle of 72° (Figure 10).

Fig. 9.

As manufactured rings with standard support structure. The arrow marks defects on one side of the ring shank

Fig. 10.

Critical regions with possible excessive heating are shown in red

In order to understand the problem, the additive manufacturing process was interrupted at a height of 7 mm, which is in the problematic region of the ring shank. An SEM investigation of the last built layer (Figure 11) indicates a perfect surface on the left side of ring. On the right side however, the surface appears highly porous. The surface is uneven with significant balling of the melt pool. The view on the outer surface of the ring shank and a metallographic section through the centre of the ring shank (Figure 12) show powder particles that stick to the surface. The powder particles themselves show a layer of much finer particles indicating a kind of condensate on the surface. Local chemical analysis by EDX showed an enrichment of the condensate with the alloying components gold and indium compared to the ring shank material.

Fig. 11.

Interrupted build job at a height of approximately 7 mm: (a) surface of the left side of the ring shank according to Figure 9; (b) surface of the right side of the ring shank according to Figure 9

Fig. 12.

Detail of the surface area of the right ring shank as marked in Figure 11

4. Discussion

4.1 Laser Track Tests on Metal Sheet

Two main modes of laser-metal interaction can be distinguished (20). In the conduction mode, no vaporisation of the material occurs and the melt pool depth is relatively small (Figure 3(b)). If the laser energy increases, i.e. the speed decreases, material evaporates and the melt pool becomes significantly deeper. Figure 3(c) shows a typical example of this transition mode. The transition mode occurs over a wide range of processing parameters (20). In the keyhole mode the material under the laser is strongly heated causing more evaporation due to internal reflection of the laser light in the deep keyhole. This increases the absorption of laser light and turns the material into a black body (21). Such conditions result in very deep laser tracks (Figure 4(c)), often associated with typical keyhole porosity.

In the present study, the laser track experiments showed a certain amount of scattering in the width and depth measurements, which is a result of a change from conduction to transition mode and sometimes even to the keyhole mode. Such behaviour has been observed on different materials with different machines (22). Metallographic evaluation of such changes is quite time and material consuming. Therefore, the fraction of conduction mode was evaluated by qualitative assessment of the surface appearance of the laser tracks.

For the width, such scattering could be well described by measuring the average width over 15 mm of total track length. However, width is not much affected by changing the laser parameters. The determination of fluctuation in depth was not feasible as the amount of metallographic work would have been too much. It is known from literature (2326) that the interaction of laser energy and the formation and size of a melt pool depends on several material properties, among which reflectivity, thermal conductivity, surface tension, viscosity, enthalpy of melting, liquidus temperature and melting range are the most important. By alloying, such properties can be strongly influenced (2731). Therefore, it is not surprising that the higher alloyed materials (for example 60Pt‐Pd‐Cu alloys) showed a more pronounced effect on melting depth than the lower alloyed 95% platinum alloys. It is also not surprising that elements with strong effect on liquidus and solidus can strongly affect the melting depth even in small additions. The effects of the different alloying elements on the material properties and the resulting melting depth are discussed in the following paragraph.

The effect of the addition of melting point suppressing elements on the melting interval can be assessed based on the binary phase diagrams of platinum with these elements. However, in a multicomponent system such estimation might not be sufficient. Therefore, thermodynamic calculations of 95% platinum alloys were performed using the Thermo-Calc software package and the TCNOBL1 database (Thermo-Calc Software AB, Sweden), Figure 13(a). The diagram shows a combination of five isopleth sections of the quaternary systems in the platinum-rich corner around the liquidus-solidus region. The liquidus and the solidus line of each system are plotted using the same colour. The ternary alloy 95Pt-1.5Cu-3.5Ru is plotted for an X-value of zero. This alloy has a very small melting range (difference between solidus and liquidus temperature). If ruthenium is exchanged for one of the X elements both solidus and liquidus temperature are lowered and the melting interval increases. However, the extent of the reduction of solidus and liquidus temperature strongly depends on the element X. Indium and tin have the weakest effect on lowering solidus and liquidus temperature. The effect of zinc is slightly higher and that of gallium even more. Germanium has by far the strongest effect, especially on the solidus line, which is very much reduced for even small additions of germanium.

Fig. 13.

Thermo-Calc calculations using TC_V2022a and the TCNOBL1 database: (a) effect of the addition of low melting elements to 95Pt-1.5Cu-Ru-X alloys on the liquidus and solidus line; (b) Scheil calculation with solute trapping for a scanning speed of 100 mm s–1 for alloys 95Pt-1.5Cu-1.5Ru-2X. Dotted lines represent equilibrium cooling conditions

During the PBF-LB process, the very high cooling rate promotes the segregation of some alloying elements, which affects the actual solidus temperature. Scheil simulations consider the effect of limited diffusion in the solid phase and effects on the solidus temperature. Thermo-Calc offers a Scheil simulation with solute trapping that takes into account the conditions during additive manufacturing. The difference between equilibrium solidification (Figure 13(a)) and non-equilibrium solidification (Figure 13(b)) in terms of solidus temperature is significant. Zinc shows a relatively small difference between equilibrium and non-equilibrium solidification, because the eutectic reaction involving the PtZn phase above 1600°C (32) limits further lowering of the solidus temperature. This is supposed to limit the extension of the melt pool. Eutectic reactions also occur in the platinum-gallium and platinum-germanium systems. However, the eutectic temperatures are much lower. The lower temperature results in a much deeper melt pool.

4.2 Laser Powder Bed Fusion Parameter Optimisation

Suitable PBF-LB parameters of the chosen 951PtP1 alloy could be determined to obtain a porosity below 0.1%. The porosity is a factor of 10 lower compared to surface treated 18 karat 3N gold alloys that were produced using the same machine (9). Staiger (33) investigated the width and depth of laser tracks on metallic sheet material and found that the width and depth of a 951PtP1 alloy was comparable to austenitic stainless steel and grade 5 titanium. 18 karat palladium white gold showed slightly higher width and depth compared to 951PtP1, while 18 karat yellow and red gold showed much lower width and depth of the laser lines. The similarity of 951PtP1 to austenitic stainless steel and grade 5 titanium is due to its similar infrared light reflectivity and similar thermal conductivity.

The porosity of parts produced by PBF-LB is a function of scan speed (34, 35). At low scan speed, i.e. high-energy tendency the porosity is relatively high due to keyhole porosity. Keyholing could be achieved on 951PtP1 sheet only at extremely low scan speed (25–50 mm s–1 at 95 W) (33). According to Tang et al. (35) the lowest porosity is achieved in a medium range scan speed. For 950Pt alloys, this was achieved in the present study at 100–600 mm s–1 (hatch distance 63 μm, laser power of 95 W, Figure 8). If the scan speed is further increased, Tang et al. (35) describe an increase of porosity due to lack of fusion. This work showed lack of fusion in 951PtP1 for hatch distances below 63 μm. The previous study on 18 karat yellow gold (9) found that lack of fusion pores emerge throughout the complete range of process parameters. Fully dense gold parts could be achieved at much higher laser powers of 375 W (12).

4.3 Optimisation of the Support Structure

The condensation of material that was observed on the defective ring shank (Figure 12) requires an initial evaporation of alloying elements. This is a clear indication of localised excessive heating of the material. To identify the reason for such overheating, the process conditions were analysed in detail. It appears that the laser works from right to left during the hatch scan. The different curvature of the ring on the left and right sides relative to the laser direction results in insufficient heat dissipation on the right side of the ring shank. The laser scans from right to left. Therefore, it first encounters an unsupported powder bed with limited heat dissipation on the right side of the ring shank. As a consequence, about 50% of the ring shank cross-section (Figure 11) is locally overheated, which results in the evaporation of the lower melting elements (gold, indium) of the alloys. The left ring shank however does not suffer from such overheating because the laser starts on a well supported powder bed. On the very left side of the left ring shank the already lasered layer provides sufficient heat dissipation to prevent overheating.

In order to prevent the observed ring shank defects, sufficient heat dissipation has to be ensured on the right side of the ring shank by additional supports. The critical angle that requires additional supports was determined to be approximately 61° and 72° on the left and the right side of the ring shank, respectively. The critical angles on either side were determined by optical quality control of the rings. The supports should reach up to 6 mm and 8 mm on the left and the right side of the ring, respectively. Such regions are marked in red in Figure 10. These angles are much larger than a conventional rule of thumb that only surfaces with an angle below 45° should require supports.

Finally, all regions with smaller angles relative to the building plate were supported. Figure 14 shows the support structures before and after optimisation. With optimised supports the ring could be manufactured without defects (Figure 15). Polishing and stone setting resulted in perfect finish.

Fig. 14.

CAD model of the ring with: (a) the original support structure; and (b) the optimised support structure. Arrows indicate the additional supports

Fig. 15.

Final ring (outer diameter 23 mm) with optimised support structure: (a) after the laser powder bed fusion process; and (b) after polishing and stone setting

5. Summary and Conclusions

Experiments with laser tracks on sheet materials showed a transition of the laser-material interaction from conduction to transition mode for most of the alloys tested. The transition mode can be unstable resulting in a very large scatter of the width and depth values of the laser tracks. A stable keyhole mode was only reached for alloys that contained high amounts of germanium, gallium or tin. Laser track experiments on metal sheets allow the testing of many different alloys with reduced experimental effort. However, due to the large scatter they are difficult to evaluate and barely useful for a determination of suitable parameters for PBF-LB. They allow the effect of alloying additions on the laser-material interaction to be studied.

The additive manufacturing of 950Pt alloys by PBF-LB technology was successfully demonstrated. The optimum process parameters were a hatch distance of 63 μm and a laser speed of 100–600 mm s–1 at a laser power of 95 W (Nd:YAG laser with 1064 nm wavelength and a spot size of 30 μm). For such parameters a residual porosity below 0.1% could be reached. A smaller hatch distance resulted in gas porosity. 950Pt alloys can be processed with similar parameters to austenitic stainless steel (316L).

Jewellery ring samples were prepared with conventional support structures. However, it appeared that the design of the supports must take into account machine-specific laser scanning procedures. Additional supports were required at positions where the laser encounters an unsupported powder bed if the orientation of the parts was below approximately 72° relative to the build plate. Otherwise, excessive heating resulted in the evaporation of material causing defective surfaces. Therefore, careful design of the support structures must be considered as part of PBF-LB process optimisation.


  1. 1.
    D. Zito, A. Carlotto, A. Loggi, S. Bortolamei, A. Molinari and I. Cristofolini, ‘Latest Developments in Selective Laser Melting Production of Gold Jewelry’, in 26th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, 20th–23rd May, 2012, pp. 537 – 562 LINK
  2. 2.
    D. Zito, A. Carlotto, A. Loggi, P. Sbornicchia, D. Maggian, M. Fockele, P. Unterberg, A. Molinari and I. Cristofolini, ‘Optimization of the Main Selective Laser Melting Technology Parameters in the Production of Precious Metal Jewelry’, in 27th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2013, pp. 1 – 20 LINK
  3. 3.
    D. Zito, A. Carlotto, P. Sbornicchia, A. Molinari, I. Cristofolini, P. Unterberg and M. Fockele, ‘Optimization of SLM Technology Main Parameters in the Production of Gold and Platinum Jewelry’, in 28th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, USA, 18th–21st May, 2014, pp. 439 – 469 LINK
  4. 4.
    D. Zito, A. Carlotto, A. Loggi, P. Sbornicchia, D. Bruttomesso and S. Rappo, ‘Definition and Solidity of Gold and Platinum Jewelry Produced Using Selective Laser Melting (SLM TM) Technology’, in 29th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2015, pp. 455 – 491 LINK
  5. 5.
    D. Zito, V. Allodia, P. Sbornicchia, S. Rappo and L. Fiorese, ‘Direct 3D Metal Printing: A Trip through New Opportunities and Innovative Alloys’, in 30th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2016, pp. 473 – 514 LINK
  6. 6.
    D. Zito, V. Allodia, F. Trevisan, M. G. M. Rossini, A. Rossini and M. Mazza, ‘Potential and Innovation of the Selective Laser Melting Technique in Platinum Jewelry Production’, in 32nd The Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2018, pp. 625 – 684 LINK
  7. 7.
    D. Zito, SPA Progold, ‘Use of Gold Powder Alloys for Manufacturing Jewellery Items by Selective Laser Melting’, US Patent 10,638,819; 2020
  8. 8.
    D. Zito, E. Saccardo, P. Sbornicchia, V. Allodia and G. A. C. Arque, ‘Innovative Printing Strategy for High-Resolution Jewelry Production by Selective Laser Melting’, in 2022 Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2022, pp. 629 – 666 LINK
  9. 9.
    U. E. Klotz, D. Tiberto and F. Held, Gold Bull., 2017, 50, (2), 111 LINK
  10. 10.
    U. E. Klotz, D. Tiberto and F. J. Held, Galvanotechnik, 2019, 110, (8), 1436
  11. 11.
    D. Fletcher and F. Cooper, ‘The Precious Project: Polishing and Finishing of Additive Manufacturing (AM) Jewelry’, in 2018 Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2018, pp. 211 – 234 LINK
  12. 12.
    H. Ghasemi-Tabasi, J. Jhabvala, E. Boillat, T. Ivas, R. Drissi-Daoudi and R. E. Logé, Addit. Manuf., 2020, 36, 101496 LINK
  13. 13.
    C. Pogliani and A. Albertin, ‘Case Study of Problems and Their Solutions for Making Quality Jewelry Using Selective Laser Melting (SLM) Technology’, in 30th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2016, pp. 431 – 458 LINK
  14. 14.
    J. Strauss, ‘Additive Manufacturing of Precious Metals’, in “ASM Handbook: Additive Manufacturing Processes”, eds. D. L. Bourell, W. Frazier, H. Kuhn and M. Seifi, Vol. 24, ASM International, Materials Park, USA, 2020 LINK
  15. 15.
    T. Laag and J. Heinrich, ‘Advantages and Challenges of Platinum Group Metals Powder Processing’, in 2018 Santa Fe Symposium on Jewelry Manufacturing Technology, Met-Chem Research, Albuquerque, New Mexico, USA, May, 2018, pp. 327 – 343 LINK
  16. 16.
    U. E. Klotz and T. Drago, Platinum Metals Rev., 2011, 55, (1), 20 LINK
  17. 17.
    T. Heiss, U. E. Klotz and D. Tiberto, Johnson Matthey Technol. Rev., 2015, 59, (2), 95 LINK
  18. 18.
    U. E. Klotz, T. Heiss and D. Tiberto, Johnson Matthey Technol. Rev., 2015, 59, (2), 129 LINK
  19. 19.
    U. E. Klotz, D. Tiberto and F. Held, ‘Additive Manufacturing of 18-Karat Yellow-Gold Alloys’, in 30th Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May, 2016, pp. 255 – 272 LINK
  20. 20.
    S. Patel and M. Vlasea, Materialia, 2020, 9, 100591 LINK
  21. 21.
    B. Fotovvati, S. F. Wayne, G. Lewis and E. Asadi, Adv. Mater. Sci. Eng., 2018, 4920718 LINK
  22. 22.
    F. J. Held and U. E. Klotz, ‘Effect of Material Properties and Process Parameters in Powder Bed Additive Manufacturing’, in 2022 Santa Fe Symposium on Jewelry Manufacturing Technology, Albuquerque, New Mexico, USA, May 2022, pp. 233 – 262 LINK
  23. 23.
    Z. Li, G. Yu, X. He, S. Li, C. Tian and B. Dong, Opt. Laser Technol., 2020, 123, 105914 LINK
  24. 24.
    R. Fabbro, J. Phys. D: Appl. Phys., 2010, 43, (44), 445501 LINK
  25. 25.
    W. E. King, H. D. Barth, V. M. Castillo, G. F. Gallegos, J. W. Gibbs, D. E. Hahn, C. Kamath and A. M. Rubenchik, J. Mater. Process. Technol., 2014, 214, (12), 2915 LINK
  26. 26.
    A. M. Rubenchik, W. E. King and S. S. Wu, J. Mater. Process. Technol., 2018, 257, 234 LINK
  27. 27.
    S. Mehmood, U. E. Klotz and G. Pottlacher, Metall. Mater. Trans. A, 2012, 43, (13), 5029 LINK
  28. 28.
    S. Mehmood, U. E. Klotz, and G. Pottlacher, ‘Thermophysical Properties of the Platinum-Copper System’, EPD Congress, San Diego, USA, 27th February–3rd March, 2011, eds. S. N. Monteiro, D. E. Verhulst, P. N. Anyalebechi and J. A. Pomykala, John Wiley & Sons Inc, Hoboken, USA, 2011, pp. 167 – 173 LINK
  29. 29.
  30. 30.
    Y. Plevachuk, S. Mudry, V. Sklyarchuk, A. Yakymovych, A. Korolyshyn, I. Shtablavyy, Y. Kulyk, U. E. Klotz, C. Liu and C. Leinenbach, Int. J. Mater. Res., 2009, 100, (5), 689 LINK
  31. 31.
    Y. Plevachuk, S. Mudry, V. Sklyarchuk, A. Yakymovych, U. E. Klotz and M. Roth, J. Mater. Sci., 2007, 42, (20), 8618 LINK
  32. 32.
    Z. Moser, J. Phase Equilibria, 1991, 12, (4), 439 LINK
  33. 33.
    R. Staiger, ‘Einfluss der Prozessparameter und er Werkstoffeigenschaften bei der Additiven Fertigung von Metallischen Werkstoffen’, Bachelor Thesis, HFU Hochschule Furtwangen University, Furtwangen, Germany, 2019
  34. 34.
    H. Gong, K. Rafi, H. Gu, T. Starr and B. Stucker, Addit. Manuf., 2014, 14, 87 LINK
  35. 35.
    M. Tang, P. C. Pistorius and J. L. Beuth, Addit. Manuf., 2017, 14, 39 LINK

‘Scheil Solidification Simulations’, ThermoCalc Software AB, Solna, Sweden:


This research project was supported by the Federal Ministry for Economic Affairs and Energy (BMWi) through the AiF (IGF no. 20670N) based on a decision taken by the German Bundestag. We kindly acknowledge the support of the members of the users committee, in particular the provision of 951PtP1 alloy powder and 3D CAD models by C. Hafner GmbH+Co.KG and Christian Bauer Schmuck GmbH+Co.KG, respectively. We thank our colleagues at fem for their contribution, namely Dario Tiberto and Daniel Blessing for additive manufacturing trials, metallography and SEM.

Supplementary Information

‘Scheil Solidification Simulations’, ThermoCalc Software AB, Solna, Sweden:

The Authors

Ulrich E. Klotz studied Physical Metallurgy at the University of Stuttgart, Germany, and earned his PhD from The Swiss Federal Institute of Technology (ETH) Zurich, Switzerland. From 1999 to 2007 he worked at the Swiss Federal Laboratories for Materials Testing and Research (Empa) in Dübendorf, Switzerland. Since 2007 he is Head of the Department of Physical Metallurgy at the Research Institute for Precious Metals and Metals Chemistry (fem), Germany. His research interests are thermodynamics and phase diagrams and processing technology including investment casting and additive manufacturing of precious metal alloys.

Frank König did an apprenticeship as material tester metal technology at vothec Labor GmbH and studied materials engineering at Aalen University, Germany. Now he is studying Metallurgy at the University of Leoben, Austria. Since 2019 he is responsible for the Additive Manufacturing Laboratory in the Department of Physical Metallurgy at the fem. His research interests are metallurgical processes including additive manufacturing and metal atomisation. Furthermore the process monitoring and optimisation with data analytics.

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