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Article

Influences of Different Selective Laser Melting Machines on the Microstructures and Mechanical Properties of Co–Cr–Mo Alloys

by
Atsushi Takaichi
1,*,
Yuka Kajima
1,
Hein Linn Htat
2 and
Noriyuki Wakabayashi
1
1
Department of Advanced Prosthodontics, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8549, Japan
2
Department of Prosthodontics, Faculty of Dentistry, Chulalongkorn University, Bangkok 10330, Thailand
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(15), 6576; https://doi.org/10.3390/app14156576 (registering DOI)
Submission received: 4 July 2024 / Revised: 16 July 2024 / Accepted: 26 July 2024 / Published: 27 July 2024
(This article belongs to the Special Issue Three-Dimensional (3D) Printing in Dentistry: Technologies, Influencing Factors and Applications)
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Abstract

:
Dental prostheses have been fabricated using various selective laser melting (SLM) machines; however, the impact of the type of machine on the microstructure and mechanical properties of Co–Cr–Mo alloys remains unclear. In this study, we prepared samples using two SLM machines (the small M100 and mid-sized M290) with different beam spot sizes (40 and 100 µm, respectively). The microstructures and tensile properties of the heated (1150 °C for 60 min) and as-built samples were evaluated. The grain sizes of the M100 samples were smaller than those of the M290 samples due to the small beam spot size of the M100 machine. Both heated samples exhibited recrystallized equiaxed grains; however, the amount of non-recrystallized grains remaining in the M290 sample exceeded that in the M100 sample. This suggests that the M100 samples recrystallized faster than the M290 samples after heating. The elongation of the M100 samples was higher than that of the M290 samples in the as-built and heated states, owing to the smaller grain size of the M100 samples. A comparison of the M100 and M290 SLM machines indicated that the M100 was suitable for producing dental prostheses owing to its good elongation and rapid recrystallization features, which shorten its post-heat-treatment duration.

1. Introduction

Selective laser melting (SLM), a powder-bed fusion technique, is used in the dental field for fabricating dental prostheses such as crowns, bridges, and frameworks of removable dentures [1,2] because it enables the rapid, low-cost, semi-automatic, and highly accurate fabrication of intricate products [3]. Co–Cr alloys are extensively used in fabricating dental prostheses [1] owing to their excellent mechanical properties and biocompatibility [4]. Compared to conventional casting methods, SLM-fabricated samples exhibit superior mechanical properties and corrosion resistance because of their unique fine cellular or columnar dendritic microstructures, which are formed through repeated rapid heating and cooling during fabrication [5,6,7]. Additionally, SLM builds exhibit smaller grain sizes compared to conventional casting, which contribute to improved mechanical properties. These microstructure patterns are created by the coupled effects of solid/liquid interface instability and melt hydrodynamic instability [8]. In such patterns, the Cr and Mo contents at the cellular or columnar dendritic boundary are higher than those at the center of the dendrite, contributing to improved corrosion resistance [5,7]. However, rapid heating and cooling during fabrication induce thermal gradients, resulting in high levels of residual stress [9]. Consequently, SLM-fabricated parts generally require post-heat treatment to relieve the residual stress [10].
The heat-treatment conditions affect the mechanical properties of Co–Cr alloys produced by SLM. Yan et al. reported that heat treatment at 1100 °C, rather than 880 °C, resulted in higher elongation in a Co–Cr alloy fabricated by the EOS M100 [11]. Therefore, 1100 °C is more suitable for fabricating dental prostheses requiring toughness, such as frameworks for removable partial dentures (RPDs) [12]. A study reported that Co–Cr alloy heated at 750 and 900 °C induced transformation of the γ phase to ε phase, resulting in high-proof strength and hardness; however, the elongation decreased [3,11]. Heat treatment at 1150 °C for ≥45 min was reported to change the grain structure from columnar to equiaxed, resulting in a recrystallized microstructure with excellent strength and ductility [13]. Two types of EOSINT CoCr powder are commercially available for use in dental prostheses: one comprises a Co–Cr–Mo-based alloy (MP1) suitable for metal frameworks, while the other contains a Co–Cr–Mo–W-based alloy (SP2), which meets the chemical and thermal requirements of the ISO 9693 standard for CoCr porcelain fused to metal in dental materials. The manufacturer of this powder has recommended different heat treatments for each type. SP2 has been recommended to be heated at 750 °C for 60 min to relieve the residual stress, while MP1 has been recommended to be heated at 1150 °C for six hours to relieve the residual stress and undergo recrystallization. However, continued heat treatment after recrystallization leads to coarsening of the grains and subsequent deterioration in the mechanical properties [2,13]. In our previous studies on MP1, we reported that for dental prostheses that are not typically large, heat treatment at 1150 °C for ~60 min was sufficient for recrystallization and achieving excellent mechanical properties [2,13].
Fitness, defined as the gap between RPD frameworks and cast, is comparable for RPDs fabricated by SLM using the EOS M270 and those that are conventionally cast [14]. The trueness of RPD frameworks fabricated by SLM using the M270 is superior to that of cast RPD frameworks [15]. Additionally, clasps fabricated by SLM using the M270 exhibit less initial retention force degradation than those fabricated by casting and have shown superior survival rates in fatigue tests [15]. Therefore, SLM is considered a promising alternative method for fabricating partial dentures compared to casting.
To date, various SLM machines, such as the EOSINT M100, M270, and M280, Concept Laser M1 cusing, Mlab, PM100 Dental, the PXM system, SLM Realizer, and SLM Realizer 2, have been used in fabricating metal frameworks for RPDs and tooth-supported prostheses [16], with the EOSINT machines being the most frequently used [17]. In Japan, the Japanese Pharmaceutical Affairs Law approved the M100, M270, and M290 SLM machines manufactured by EOS (Krailling, Germany) for use in RPD fabrication [17]. The M290 is a mid-sized SLM machine (2500 × 1300 × 2190 mm3) with a laser power and beam spot size of 400 W and 100 µm, respectively. The M100 is a small machine (800 × 950 × 2250 mm3) suitable for a dental laboratory with limited space, with a small laser spot (beam spot size: 40 µm), providing excellent detail resolution that is ideal for fabricating highly complex dental devices. Both machines are widely used globally; however, their parameter settings differ, and their influences on the characteristics of the fabricated devices remain unclear.
Several studies comparing the mechanical properties of Co–Cr alloys fabricated using different SLM machines have been reported [18,19,20]. However, these studies used different Co–Cr powders, machines manufactured by different companies, and varying scanning strategies. It has been reported that the powder size distribution considerably influences the microstructures and mechanical properties [21]. Li et al. reported that powder granulometry remarkably influenced heat-treated Co–Cr alloys when using a different powder size distribution because of the different extents of recrystallization occurring between samples with different powder size distributions [21]. Apart from the powder size, differences in the chemical composition also affect the microstructures and mechanical properties. In addition, the scanning strategy impacts the cooling rate [22], which affects the ratio of face-centered-cubic (FCC) and hexagonal close-packed crystal structures [23]. Therefore, the results are influenced by various complex factors, such as the chemical composition of the alloy powder, SLM operating parameters, and scanning strategy [24].
This study aims to investigate the influence of different SLM machines on the mechanical properties and microstructures of the fabricated alloys. The investigation is conducted under conditions with minimal confounding factors by using SLM machines (M100 and M290) from the same company, the same alloy powder, and the same scanning strategy. The null hypothesis is that the type of SLM machine would not influence the mechanical properties of the Co–Cr alloys. The results obtained from this study are expected to serve as a criterion for dentists and dental technicians when selecting SLM machines for fabricating dental prostheses using SLM.

2. Materials and Methods

The flowchart of all the experiments is shown in Figure 1.

2.1. Specimen Preparation

Commercially available Co–Cr–Mo alloy powder (MP1, EOS, Krailling, Germany) was utilized to fabricate dumbbell-shaped samples (with longitudinal axes parallel to their build directions, as shown in Figure 2) using two SLM machines (EOSINT M100 and M290, EOS, Krailling, Germany) equipped with fiber lasers (n = 12 for each machine). The dumbbell-shaped samples with conical shoulders were designed using a 3D software program (Rhino 7, Rhinoceros, Seattle, WA, USA) according to the ISO 22674 standard with a 3 mm diameter and an 18 mm parallel section [25]. The chemical composition of the alloy powder provided by the manufacturer is shown in Table 1 [7], and its morphology is shown in Figure 3. The particle size distribution of the metal powder follows a normal distribution, with D10, D50, and D90 values of 13, 25, and 42 μm, respectively [26]. The SLM machines were operated using standard deposition parameters for MP1, with laser powers of 200 and 400 W employed when using the M100 and M290 under Ar and N2 atmospheres, respectively. The different atmospheres in M100 and M290 are due to the specifications provided by their manufacturer. However, it has been reported that as long as the oxygen level does not exceed a threshold value, the choice between N2 or Ar atmospheres does not significantly affect the microstructure or mechanical properties [27]. In this study, fabrication was performed at oxygen levels ≤1000 ppm. The laser scanning pattern was rotated by 67° around the z-axis between adjacent layers. Half of the samples (n = 6) were heat treated under an Ar atmosphere using the following procedure: (1) heating the furnace from room temperature to 600 °C, (2) keeping the sample in the furnace at that temperature for 30 min, (3) heating to 1150 °C, (4) maintaining for one h, (5) turning off the furnace and opening the furnace door, and (6) waiting until the samples cooled to room temperature (Figure 4). The heat-treated samples were subjected to blasting to remove the surface oxide film using an airborne abrasion (Jet Blast III; J. Morita Corp., Tokyo, Japan) at a pressure of 0.4 MPa using 50 μm Al2O3. The remaining half of the samples were not subjected to heat treatment; this group was denoted as “as-built”.

2.2. Mechanical Properties

Tensile tests were performed using a universal testing machine (Instron universal testing machine AG-2000B, Shimadzu, Kyoto, Japan; n = 5 for each condition) at an initial strain rate of 1.1 × 10−3 s−1. The strain values were measured by non-contact strain measurement using a high-speed CCD camera (XC-75, Sony, Tokyo, Japan). The mean values of the ultimate tensile strength (UTS), 0.2% proof strength (0.2% PS), and elongation were calculated from the obtained data. The values were statistically analyzed using the Student’s t-test, and differences among the data with p-values of <0.05 were considered statistically significant.

2.3. Microstructural Analysis

To examine the microstructures, the remaining samples (n = 1 for each condition) were cut in directions transverse to their longitudinal directions with a low-speed diamond cutter to form cylindrical samples (diameters: ~3 mm; heights: ~1 mm). The cylindrical samples were polished using waterproof emery paper (up to 1000 grit), a 9 μm diamond, and a 0.04 μm colloidal silica suspension, then etched with an H2SO4/CH3OH (5:95) solution at 16–20 V for 1 s. The microstructures were then evaluated using confocal laser scanning microscopy (CLSM; OLS4000, Olympus, Tokyo, Japan) at the macroscale and scanning electron microscopy (SEM) at the microscale with energy-dispersive X-ray spectroscopy (EDS; S-3400NX, Hitachi, Tokyo, Japan) at an accelerating voltage of 15 kV. The crystallographic orientation was examined via electron backscatter diffraction (EBSD; Gatan, Pleasanton, CA, USA) using a field-emission scanning electron microscope (XL-30 FEG, Philips, Amsterdam, Netherlands) with a step size of 1.1 μm, a working distance of 15 mm, and an accelerating voltage of 15 kV. The TSL OIM 7 software (TSL Solutions KK, Anan, Japan) was used to obtain the inverse pole figure (IPF) maps, phases, grain boundaries (GBs), kernel average misorientation (KAM), and phase maps, as well as the grain size distribution. The grain sizes were measured using the data for all complete grains in a single map (500 μm × 500 μm) [9]. Phase identification was performed using X-ray diffraction (XRD; MiniFlex, Rigaku, Tokyo, Japan) in the 2θ scanning range of 40–55° with the diffractometer operating at 40 kV and 40 mA with Cu Kα radiation, a step size of 0.02°, and a dwell time of 1.0 s per increment.

3. Results

3.1. Microstructural Analysis

Figure 5a–d present the CLSM images of the M100 and M290 samples. The as-built M100 and M290 samples exhibit laser-melted tracks formed via an alternating 67° filling strategy. The widths of the tracks in the M100 and M290 samples are ~40–70 and 80–120 µm, respectively, corresponding to the hatching distances (which are related to the laser spot sizes). After heating, the laser-melted tracks are no longer observed, but the GBs are clearly observed.
Figure 6a–d illustrate the SEM images of the M100 and M290 samples. The as-built samples display different layers, with several containing cellular dendrites and others featuring columnar structures due to the alternating 67° filling strategy. In contrast, the heated M100 and M290 samples exhibit columnar precipitates along their GBs, and the difference in the precipitate sizes of the two samples is negligible.
Figure 6c,d and Table 2 present the SEM images and the results of the EDS point analyses of the heated M100 and M290 samples. The point analyses of the matrices and precipitates of the samples were performed at three different locations on the samples. In the M100 and M290 samples, the contents of Co are higher in the matrices compared to those in the precipitates. Conversely, the C, Cr, and Mo contents are higher in the precipitates than those in the matrices, indicating the formation of carbide (M23C6) precipitates [7].
Figure 7 shows the XRD patterns of the M100 and M290 samples. The observed peaks correspond to the FCC γ-Co phase. As-built M290 exhibits a strong γ (200) orientation, indicating the presence of a {200}-texture.
Figure 8 plots the GBs, IPFs, phases, and KAM maps (transverse to build directions) as measured using EBSD. Both as-built samples exhibit large fractions of low-angle boundaries (LABs; θ ˂ 15°), high-KAM regions (green areas), and small fractions of Σ3 twin boundaries. The LAB fraction and high-KAM regions in the M100 sample are larger than those in the M290 sample. In contrast, the heated samples display equiaxed grains with multiple Σ3 twin boundaries and drastically reduced LAB fractions. The KAM values of the heated samples are significantly lower than those of the as-built samples; however, small numbers of grains with high KAM values remain, particularly in the M290 samples.
Figure 9 shows the EBSD-determined grain-size distributions of the samples. The grains in the M100 samples are finer than those in the M290 samples in the as-built and heated states. After heating, the grain sizes of both samples increased.

3.2. Mechanical Properties

The results of the tensile studies are listed in Table 3, and the stress-strain curves of representative samples for each group are shown in Figure 10. In the as-built and heated states, the degrees of elongation of the M100 samples significantly exceed those of the M290 samples. Conversely, no significant differences in the 0.2% PS and UTSs of M100 and M290 are detected. After heating, the 0.2% PS and UTSs of both samples decrease, whereas their degrees of elongation increase.

4. Discussion

In this study, the degrees of elongation of the M100 samples significantly exceed those of the M290 samples in the as-built and heated states; therefore, the null hypothesis was rejected.
The main differences between the EOS M100 and M290 machines are as follows: the M100 uses a fiber laser with a power of 200 W and a diameter of 40 μm, whereas the M290 employs a fiber laser with a power of 400 W and a diameter of 100 μm. Consequently, the M290 exhibits higher output power and a larger laser track, leading to the formation of coarser grains. In contrast, the grains in the samples prepared using the M100 are finer due to its narrower laser track and lower laser power. These finer grains in the M100 samples contribute to their higher degrees of elongation in both the as-built and heated states [28,29]. The tendency of precipitates in M100 and M290 did not show significant differences. Therefore, it can be said that the influence of precipitates on ductility is minimal. XRD results showed that in as-built states, M290 samples have a stronger {200}-texture compared to the M110 samples. Thus, M290 samples can have stronger anisotropy. However, after heat treatments, both samples did not exhibit {200}-texture; thus, it is anticipated that both samples are homogenized, and the influence of anisotropy will be almost negligible in both M100 and M290 samples after heat treatment. The presence of internal porosity in Co–Cr alloys fabricated using SLM is a critical concern for biomedical materials, as it can reduce mechanical properties and increase susceptibility to corrosion. The density of the fabricated samples is influenced by process parameters such as laser power, scanning speed, layer thickness, and scanning pitch, and optimal parameters can achieve a density of over 97% [30]. Additionally, the scan strategy significantly affects the density of metal samples fabricated by the SLM process. The chessboard scan strategy rotated by 45° every layer decreases the internal porosity of Co–Cr alloy up to 0.1% [31]. The strategy of rotating the irradiation by 67° for each layer effectively eliminates pores formed in the lower layers, creating a high-density Mg alloy (close to 99%) [32]. In this study, internal porosity was not detected in the samples even under examination using an optical microscope, which suggests fully dense samples were obtained. This is attributed to the specimen preparation conditions applying the optimized parameters recommended by the manufacturer with a 67° rotation scan strategy. However, it has been reported that even a small amount of internal porosity was observed in metal frameworks for removable partial dentures with complex geometry fabricated by SLM [33]. This suggests that complete control of internal porosity may be challenging and warrants careful attention for clinical application.
Following heating, we observed a significant reduction in the 0.2% PS, a decrease in the UTS, and an increase in elongation, accompanied by a drastic increase in the rate of twins (Σ3 boundaries). This indicates that recrystallization occurs with the M100 as well as the M290 [3]. However, the recrystallization of the M100 samples is faster than that of the M290 samples, as high KAM values are still observed for several grains of the heated M290 samples. The KAM values indicate the differences in crystal orientations of adjacent measurement points and are typically used to evaluate residual plastic strains and dislocation density [34,35,36]. Recrystallization is traditionally defined as a phenomenon in which the internal energy accumulated due to plastic deformation is released, and new crystal grains are formed when metallic materials are heated to high temperatures. The energy required for this process primarily consists of the stored dislocation energy from plastic deformation. During the SLM process, rapid melting and heating cause residual strain accumulation and an increase in dislocation density at the grain boundaries, similar to plastic deformation. This increase in dislocation density during the SLM process elevates the internal energy [33], which serves as the driving force for recrystallization [35,37]. In this study, the as-built M100 samples displayed narrower laser-melted tracks owing to the smaller beam spot size of the M100. These narrower tracks induce higher KAM values (i.e., higher residual plastic strains and dislocation density) in the as-built M100 samples compared to the as-built M290 samples. This is because the number of melting and solidification steps occurring in the same area is higher in the M100 samples than in the M290 samples. The higher residual strains and dislocation density within the as-built M100 samples lead to a stronger driving force for recrystallization, and the faster recrystallization of the M100 samples reduces the required heating time after fabrication. The mechanical property values obtained in this experiment were similar to those in previous studies, demonstrating high strength and high ductility and fully meeting the requirements of the ISO standards [3,25,26,38]. Under the heat treatment condition of 750 °C, both the ultimate tensile strength (UTS) and 0.2% proof stress (PS) are higher compared to those at 1150 °C, while elongation decreases [3,26,38]. This is attributed to the increased proportion of the hexagonal close-packed (HCP) phase at 750 °C. These findings suggest the importance of selecting heat treatment conditions based on the prioritized mechanical properties required for dental prostheses.
Several SLM machines are commercially available, each with varying laser types, scan speeds, and focus diameters [16]. In this study, the influences of different machines with different technical specifications on the mechanical properties and microstructures were evaluated. Although the samples fabricated using EOS M100 and M290 displayed sufficient mechanical properties for use as dental prostheses, their mechanical properties and microstructures exhibited different trends. The M100 machine, being small, is suitable for fabricating relatively small devices, such as dental prostheses, and its small laser spot with good detail resolution is favorable for fabricating highly complex components. Furthermore, fine-grained microstructures and excellent elongation have been realized in this study. However, the number of M100 samples that can be fabricated in a batch is fewer than that of M290 samples; therefore, the time efficiency and order volume for dental prostheses should also be considered. Additionally, further investigations are required to compare the dimensions and fitness accuracies of the dental prostheses fabricated using both machines.

5. Conclusions

This study evaluated the mechanical properties and microstructures of Co–Cr–Mo alloys fabricated using two SLM machines (EOS M100 and M290). The M100, with a 40 µm laser spot size, produced narrower laser-melted tracks compared to the 100 µm laser spot size of the M290. Consequently, the grains in the M100 samples were finer than those in the M290 samples, resulting in higher degrees of elongation in the former. Additionally, the M100 samples stored increased residual strains during fabrication due to the narrower laser-melted tracks, leading to faster recrystallization compared to the M290 samples. These findings suggest that the EOS M100, with its smaller laser spot, is more suitable for producing dental prostheses that require a high level of toughness, such as clasp-retained removable partial dentures or long-span fixed prostheses.

Author Contributions

Conceptualization, A.T. and Y.K.; methodology, A.T.; formal analysis, A.T.; investigation, A.T., Y.K., and H.L.H.; resources, A.T.; data curation, A.T., Y.K., and H.L.H.; writing—original draft preparation, A.T.; writing—review and editing, A.T. and Y.K.; visualization, Y.K.; supervision, A.T.; project administration, N.W.; funding acquisition, Y.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Grants-in-Aid for Fundamental Scientific Research [grant numbers 22KJ1199 and 21K17058] from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Dataset available on request from the authors.

Conflicts of Interest

The authors declare that they have no competing financial interests or personal relationships that may have influenced the work reported in this study.

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Figure 1. Flowchart of the experiment design.
Figure 1. Flowchart of the experiment design.
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Figure 2. Samples on a base plate. The green plane indicates the direction of the cutting plane for microstructural characterization.
Figure 2. Samples on a base plate. The green plane indicates the direction of the cutting plane for microstructural characterization.
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Figure 3. Morphology of the powder used in the SLM samples.
Figure 3. Morphology of the powder used in the SLM samples.
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Figure 4. The heat treatment procedure of the samples.
Figure 4. The heat treatment procedure of the samples.
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Figure 5. Specimen microstructures. CLSM images of as-built (a) M100, (b) M290 heated, (c) M100, and (d) M290 samples.
Figure 5. Specimen microstructures. CLSM images of as-built (a) M100, (b) M290 heated, (c) M100, and (d) M290 samples.
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Figure 6. SEM images of as-built (a) M100, (b) M290 heated, (c) M100, and (d) M290 samples. (c,d) The asterisks indicate the analyzed locations of Co, Cr, Mo, and C contents (mass.%) determined using EDS, as shown in Table 2.
Figure 6. SEM images of as-built (a) M100, (b) M290 heated, (c) M100, and (d) M290 samples. (c,d) The asterisks indicate the analyzed locations of Co, Cr, Mo, and C contents (mass.%) determined using EDS, as shown in Table 2.
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Figure 7. XRD patterns of the M100 and M290 samples.
Figure 7. XRD patterns of the M100 and M290 samples.
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Figure 8. EBSD maps of as-built (a–d) M100, (e–h) M290 heated, (i–l) M100, and (m–p) M290. Samples: (a,e,i,m) IPFs, (b,f,j,n) GBs, (c,g,k,o) KAM maps, and (d,h,l,p) phases.
Figure 8. EBSD maps of as-built (a–d) M100, (e–h) M290 heated, (i–l) M100, and (m–p) M290. Samples: (a,e,i,m) IPFs, (b,f,j,n) GBs, (c,g,k,o) KAM maps, and (d,h,l,p) phases.
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Figure 9. Grain-size distributions of as-built (a) M100 and (b) M290 and heated (c) M100 and (d) M290 samples.
Figure 9. Grain-size distributions of as-built (a) M100 and (b) M290 and heated (c) M100 and (d) M290 samples.
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Figure 10. Stress-strain curves of the representative Co–Cr–Mo alloy samples.
Figure 10. Stress-strain curves of the representative Co–Cr–Mo alloy samples.
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Table 1. Chemical composition of the Co–Cr–Mo alloy powder in units of mass (%).
Table 1. Chemical composition of the Co–Cr–Mo alloy powder in units of mass (%).
AlloyCoCrMoSiMnFeCNi
MP160–6526–305–7<1.0<1.0<0.75<0.16<0.1
Table 2. Co, Cr, Mo, and C contents (mass%) of the heated samples were determined using EDS. The analyzed locations are shown in Figure 6c,d as asterisks.
Table 2. Co, Cr, Mo, and C contents (mass%) of the heated samples were determined using EDS. The analyzed locations are shown in Figure 6c,d as asterisks.
Matrix
(mass.%)		CoCrMoCPrecipitates
(mass.%)		CoCrMoC
*163.2728.456.411.87*747.0134.2912.656.05
*263.0528.296.542.11*839.6137.8214.617.69
*363.1628.536.471.85*937.9937.6717.716.62
*463.4928.26.441.87*1043.735.4814.086.74
*563.0128.636.641.72*1145.6834.4212.576.33
*663.2628.336.51.85*1245.9435.412.296.36
Table 3. Tensile properties of the samples. The same letter in the same row indicates no significant differences.
Table 3. Tensile properties of the samples. The same letter in the same row indicates no significant differences.
PropertiesAs-BuiltHeat-Treated
M100M290M100M290
UTS (MPa)1210 a (24)1214 a (38)1131 A (17)1143 A (37)
0.2% PS (MPa)869 a (18)873 a (37)686 A (5)682 A (18)
Elongation (%)18.6 a (0.5)15.5 b (1.2)26.0 A (1.5)23.6 B (1.4)
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MDPI and ACS Style

Takaichi, A.; Kajima, Y.; Htat, H.L.; Wakabayashi, N. Influences of Different Selective Laser Melting Machines on the Microstructures and Mechanical Properties of Co–Cr–Mo Alloys. Appl. Sci. 2024, 14, 6576. https://doi.org/10.3390/app14156576

AMA Style

Takaichi A, Kajima Y, Htat HL, Wakabayashi N. Influences of Different Selective Laser Melting Machines on the Microstructures and Mechanical Properties of Co–Cr–Mo Alloys. Applied Sciences. 2024; 14(15):6576. https://doi.org/10.3390/app14156576

Chicago/Turabian Style

Takaichi, Atsushi, Yuka Kajima, Hein Linn Htat, and Noriyuki Wakabayashi. 2024. "Influences of Different Selective Laser Melting Machines on the Microstructures and Mechanical Properties of Co–Cr–Mo Alloys" Applied Sciences 14, no. 15: 6576. https://doi.org/10.3390/app14156576

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