Quantitative investigation of thermal evolution and graphitisation of diamond abrasives in powder bed fusion-laser beam of metal-matrix diamond composites

ABSTRACT Preventing the thermal damage of diamond abrasives is the major challenge of diamond composites in the field of super-hard tools by laser additive manufacturing. In the presented work, we established a quantitative framework to accurately evaluate the thermal damage behaviour and the relevant microstructure-performance characteristics, by using CuSn10-diamond composite by powder bed fusion-laser beam (PBF-LB). By simulating the thermal history of diamond in the molten pool and microstructure characterisation, the critical temperature of 1491.6°C of diamond graphitisation was obtained. Below the critical temperature, the composite with no diamond-graphitisation exhibited abrasive wear and wear loss rate below 0.01%. The increasing temperature led to the aggravation of graphitisation, which ID: IG value changed from 2.00 to 0.57 with the temperature increasing from 1491.6°C to 1896.1°C, resulting in wear mechanism changing from adhesive wear to three-body abrasion, with the wear loss rate from 0.01% to 0.73%. Integrating the results of simulation, microstructures and wear properties, the graphitisation threshold of diamond in PBF-LB was revealed and the quantitative relationship of ‘PBF-LB parameters - Temperature - Graphitisation degree - Wear resistance’ of the metal-matrix diamond composites was established.


Introduction
Super-hard diamond composite plays an irreplaceable role in the precision manufacturing of hard and brittle materials owing to its excellent hardness and wear resistance.In recent years, owing to the development of aerospace industry, electronic communication and high-end manufacturing technologies, stringent requirements have been implemented for the precision grinding of high-performance titanium alloys for aerospace applications, carbon fiber composite materials, electronic communication 3C ceramics, high-end chips and other materials that are difficult to process (Lv et al. 2018).Laser additive manufacturing (LAM) can be employed (Peng et al. 2021) to form components with three-dimensional structures and complex shapes via the layer accumulation of materials.This approach has the characteristics of a large design space, simple procedure and high material utilisation rate and provides a new means of achieving structure-function integrated manufacturing of diamond abrasives tools (Gu et al. 2021), such as chip-holding holes and inner flow channel structures, which are important means of improving the performance of diamond tools with high precision, high efficiency and low thermal processing (Wu et al. 2019;Tian et al. 2019).
The performance of metal-matrix diamond composites by LAM is significantly affected by interaction between diamond and laser ormolten pool, due to the unique characteristics of diamond.
On the one hand, diamonds interact with lasers direct irradiation.When diamond particles are directly irradiated by a high-energy laser beam, numerous electrons are ionised and graphitisation transformation occurs (Olejniczak et al. 2019).Thus far, laser machining is used in engineering applications to polish and cut diamond, mostly by using femtosecond and picosecond pulse lasers to process diamond (Cai et al. 2020;Zhang et al. 2021b;Li et al. 2020).
On the other hand, diamond is affected by the contact of the high temperature molten pool during LAM.Owing to the development of additive manufacturing, the metal-matrix diamond composites fabricated by LAM has gradually emerged as a research focus, such as powder bed fusion-laser beam (PBF-LB), laser welding and laser cladding.
However, due to the thermal instability of diamond, the thermal damage such as oxidation, graphitisation and ablation, are likely to occur when diamond contact with high temperature molten pool.Several studies (Fang et al. 2020;Su et al. 2020;Zhang et al. 2021a) have shown that graphitisation occurs due to direct laser irradiation in diamond composites fabricated by LAM.More often, though, the thermal damage of diamond happened during the direct contact with the molten pool.The rapid melting and an uneven energy distribution of the laser Gaussian heat source in LAM lead to an extremely unbalanced temperature field in the molten pool.As the instantaneous temperature can exceed 2000°C, the diamond particles are subjected to severe high temperature heat conduction and thermal shock.Zhou, Li, and Gao (2022) found that the remelting, heat accumulation and secondary heating occurring in multi-track scanning increased the thermal damage to diamond.Daniel et al. (Rommel et al. 2016(Rommel et al. , 2017) ) studied the interfacial reactions of diamond and molten metal, showing that thermal damage and interfacial reactions occurred only in the diamond particles in contact with the molten pool, not in the diamond particles directly irradiated by the laser.Iravani et al. (2012) found that the presence of Fe and Ni as the catalyst, would aggravate the graphitisation of diamond.
Apparently, the thermal damage behaviour of diamond become the key factor for LAM technologies to be widely applied in the fabrication of diamond composite.However, the research on the thermal evolution of diamond particles and the damage mechanism during LAM is rarely reported.In the presented study, CuSn10-diamond composites were prepared by employing PBF-LB technology.The CuSn10 alloy has no graphitisation catalyst or carbide-forming elements, therefore, the effect on thermal damage of diamond can be focused on the high temperature molten pool.The thermal evolution of diamond throughout the PBF-LB process was systematically investigated by building a simulated temperature field of single diamond particles.The effect of the molten pool temperature on the graphitisation of diamond abrasives was described quantitative and verified by characterisations of microstructures and wear properties.The quantitative relationship of 'PBF-LB parameters-Temperature of diamond abrasives-Graphitization degree-Wear resistance' of the diamond composites were established.This study not only reveals the thermal evolution and damage behaviour of diamond abrasives by PBF-LB, but also provides a theoretical model for the fabrication of metal-matrix diamond composites via LAM technologies.

The feedstock and PBF-LB
The gas-atomised CuSn10 alloy powders (15-53 μm) and diamond particles (MDB4, 75-90 μm) a were used as the feedstock, and the morphology are shown in Figure 1.The CuSn10 alloy powders has good sphericity and fluidity, which is beneficial to efficient spreading during PBF-LB.The alloy powders and diamond particles were uniformly mixed by a 3D mixer for 5 h, with 12.5 vol % concentration of diamond.The mixed powders were dried at 80°C for 24 h.The CuSn10-diamond composite samples (8 mm × 8 mm × 8 mm) were fabricated by a PBF-LBequipment (WXL-120E, Xiamen Wuxinglong Technology Co., LTD) with a continuous wave laser beam, which has an emission wavelength of 1064 nm.The laser beam has maximum power of 500 W and the laser beam diameter of 50 μm.The composites were fabricated on the pure copper build platform (116 mm × 116 mm × 20 mm).During the PBF-LB process, the temperature of the substrate was maintained at about 100°C, and the oxygen content ≤400 ppm in the build chamber.The PBF-LB process parameters are listed in Table 1.And the corresponding laser energy densities were calculated according to following equation: where P is the laser power, L is the layer thickness, H is the hatch space, and v is the scanning speed.And the samples were cut from the substrate parallel to the X-Y plane by wire electrical discharge machining.

Numerical model of LAM
The ANSYS Workbench finite element software was used to simulate the temperature distribution of the diamond particle during PBF-LB, the specific steps of the finite element modelling are shown in Supplementary Information.The properties of the materials, including density, melting temperature, thermal conductivity, specific heat, were determined in JMatPro software, as shown in Table S1.
The heat transfer governing expression was used by the 3D transient heat conduction equation in a thermodynamically isotropic material.The loaded heat source is a moving Gaussian heat source, which is a main heat source model for most of simulations in laser processing (AlMangour et al. 2018;Yan et al. 2018).
The model geometry consisted of a mixed powder bed on a pure copper build platform.The CuSn10 alloy powder bed model with size of 1000 μm × 100 μm × 4000 μm; the size of diamond particles model is 80 μm × 80 μm × 80 μm cube with eight corners removed and the diamond particles model is embedded in the powder bed model.

Microstructures and properties characterisation
The microstructure and chemical composition of the feedstock and PBF-LBed samples were analysed by scanning electron microscope (SEM) with back-scattering mode (FEI Quanta FEG 250, Czech) equipped with an energy dispersive spectrometry (EDS) probe.The Archimedes method was used to measure the real density of the samples.The relative density was calculated by dividing the real density by the theoretical one.X-ray diffractometry (XRD, Bruck D8 Advance, Germany) with Cu-Ka radiation at 30-100°and 8°/min was used to analyse the phase structures of the composite samples.
The graphitisation of the diamonds was analysed by the Renishaw in Via Raman microscope system with 532 nm of wavelength, 500-2000 Raman shift/cm -1 of detection range.The wear properties were tested by the high-speed reciprocating friction testing machine with a friction time of 900 s, 50 N loading, 15 Hz frequency, and a 5 mm stroke at room temperature and the Si 3 N 4 balls (6 mm diameter) were used as counterparts.The NanoMap500DLS dual-mode profiler was used to investigate wear scar profiles in two dimensions.

PBF-LB formability of the CuSn10-diamond composites
Figure 2 shows the PBF-LB formability of the CuSn10diamond composites.The formation of balling is caused by that, the diamond particles increase the viscosity of the molten metal and limit its fluidity, and there is poor wettability between the CuSn10 alloy melt and diamond (Constantin et al. 2021).According to the balling degree, the samples can be divided to three categories: . The samples with spheroidised sizes of less than 500 μm were defined as well-formed in Figure 2(b). .The samples with spheroidised sizes of more than 500μm and having clear pits and slag were defined as poor-formed in Figure 2(c). .The samples that fell off directly from the substrate because of warping, cracking, or powder scraping during forming were defined as no-formed in Figure 2(d).
Considering the 29 PBF-LBed samples in Figure 2(a), as the laser power (P) increases and scanning speed (v) decreases, the higher laser energy input leads to a Table 1.PBF-LB process parameters for diamond composites.

Process parameters Values
Laser power (P)/W 120, 140,160,180,200,250, 300 Scanning speed (v)/mm/s 500, 700, 800, 900, 1100 Hatch space/mm 0.05 Layer thickness/mm 0.07 more intense flow and longer duration of the molten pool.These characteristics resulted in more severe balling and poor formation.According to the formability, the well-formed samples at 120-180 W laser power and 700-1100 mm/s scanning speed, were selected for further experimental exploration.
In addition, the well-formed samples only exhibited a relative density of 80.07-86.98%,far below many materials that pursue full density by PBF-LB (Khorasani et al. 2019).However, the porosity of diamond abrasive tools plays an important role in grinding.A porous structure has more interconnected microchannels and therefore can provide sufficient space for the grinding fluid and reduce the temperature of the grinding zone, which are beneficial for cooling and lubrication.Moreover, a porous structure increases the debris storage space (Xu, Liao, and Weng 2011;Hou et al. 2012).Therefore, unlike in the forming of metal materials through PBF-LB, the density of metal-diamond composites is not the only means of assessing the forming quality, and the >80% relative density of CuSn10-diamond composites is acceptable.

Thermal evolution of the diamond particles
Due to the extremely rapid melting-solidifying process during PBF-LB, it is difficult to experimentally detect the temperature of the molten pool.Therefore, an ANSYS finite element simulation was performed to establish the 3D temperature field model of the molten pool to clarify the influence of the molten pool temperature on the thermal evolution of the diamond particle.Taking the sample with P = 180W, v = 700 mm/s as an example, the temperature distribution of the diamond particle in molten pool at specific timing during molten pool moving forward in PBF-LB is shown in Figure 3, and it can be divided into three stages: Figure 4 presents the thermal evolution of diamond particles at different process parameters, revealing the changes in the temperatures over time.It is obvious that the two peak temperatures appeared, corresponding to Figure 4(b,c).The simulation results of diamond peak temperature under different PBF-LB parameters in Table 2 show that the second peak temperature is obviously higher than the first one because of the heat accumulation.
The relationship between temperature and process parameters was established.The laser energy density was always adopted as the key factor for the evaluation on the temperature of molten pool (Yang et al. 2018;Shi et al. 2022).However, the temperatures of diamond particles were significantly different under the same energy density.As shown in Figure 5, the laser energy densities of samples Nos. 5, 10 and 15 were the same as 57.1 J/ cm 3 , but it is obvious that the second peak temperature of diamond particles of sample 15 was the highest, reaching 1676.5°C, which was 184.9°C higher than that of sample 5. Therefore, the traditional method evaluating the molten pool or diamond temperature by laser energy density is not suitable for the fabrication of diamond composites by PBF-LB.Thus, temperature of diamond particles, rather than process parameters or laser energy density, will be used as the standard in the subsequent analysis of the thermal evolution and thermal damage of diamond.

Microstructures
In order to analyse the influence of the high molten pool temperature on the thermal damage of diamond particles, the microstructure characterisation of CuSn10-  diamond composites prepared by PBF-LB was carried out.The microstructures of the diamond particles are shown in Figure 6.According to the morphology and degree of thermal damage of the diamond, the processing window of 16 well-formed samples can be divided into three regions: Area 1 (no damage area); Area 2 (light damage area) and Area 3 (severe damage area).The highest temperatures of diamonds in the three areas are 1080.0 to 1420.1°C, 1491.6 to 1539.4°C and 1585.3 to 1896.1°C respectively.
In Area 1, the diamond particles remained intact with smooth surface and no obvious thermal damage was observed.With increasing of diamond temperature (increasing P and decreasing v), local structural transformation of diamond occurred, which were mainly reflected in the local fragmentation of diamond particles and the gradual disappearance of edges and corners (Sample Nos. 5, 11 and 16 in Area 2).In Area 3, diamond undergone a distinct structural transformation, the original hexagonal octahedral crystal morphology no longer retained and all crystal planes were coarsened (Sample Nos. 10, 14 and 15).Most of the diamond particles exhibited serious thermal damage, as mainly reflected by the cleavage fracture of the whole crystal (Sample Nos. 9 and 13).
To explore the possible thermal damage or phase transformation in the CuSn10-diamond composite samples, Nos. 8, 13 and 16 samples corresponding to the temperature of 1242.1°C,1539.4°C and 1891.1°Crespectively, were selected from no damage area, light damage area and severe damage area for XRD characterisation, as shown in Figure 7. CuSn10-diamond composite exhibited the α (Cu, Sn) solid solution and diamond phase.Since Cu or Sn does not react with C, no carbide phase was formed during PBF-LB.However, XRD is not able to identify the allotropes of carbon including sp3 hybridised diamond, sp2 hybridised graphite or amorphous carbon phases, therefore the graphitisation transformation of diamond will be further characterised by Raman.
Raman spectrum was used to identify the graphitisation of the diamond in CuSn10-diamond composites by  PBF-LB.As shown in Figure 8(a,b), diamond in the composite maintained an intact crystal morphology at1242.1°Cfrom Area 1.Only the characteristic peak of sp3 hybridised diamond at 1331.9 cm -1 was observed, inferring that no graphitisation of diamond occurred.However, the characteristic peaks of sp2 hybridised graphite at 1580 cm -1 were detected in the samples from both light and severe damage area as shown in Figure 8(c,e), demonstrating that the graphitisation of diamond particles occurred.Figure 8(c) reveals that the diamond (1343.6 cm -1 ) and graphite (1593.3cm -1 ) characteristic peaks have different degrees of deviation, which may be due to the lattice distortion caused by different rapid cooling rate during PBF-LB.Moreover, as the temperature of diamond increased, the graphitisation degree of diamond intensified.The graphite characteristic peak is clearly visible in Figure 8(e).It is shown in Figure 8(d,f) that the area ratios of I D /I G are about 1.10 and 0.57.The interfacial bonding state of CuSn10/diamond determines the retention force on the diamond and affects the performance of the composite.To explore the interfacial diffusion behaviour of CuSn10/diamond further, EDS line-scanning analysis was performed, and the results are shown in Figure 9.The diffusion zone gradually expanded with increasing temperature.When the temperature of the diamond was 1242.1°C, the interfacial diffusion zone was approximately 1 μm.When the temperature of diamond was up to 1891.1°C , the width of diffusion zone reached approximately 2.5 μm.Theoretically, there should be no phase transformation or diffusion at the interface, since the Cu and Sn do not react with the diamond showing a mechanical bonding of the CuSn10/diamond interface (Denkena et al. 2016).However, the latest research showed that the hybridisation degree of the s and p orbital electrons of the Sn atoms and the p orbital  of the C atoms is very strong that the relaxed structure with Sn atoms has a high electron enrichment ability.This characteristic is beneficial for the formation of a strong covalent interaction between the intermetallic compounds in the CuSn10 alloy and diamond (Yu et al. 2022).Moreover, due to the high temperature molten pool of PBF-LB, the free C atoms were subsequently separated from the diamond surface, which would be directly dissolved into the melt, and the solubility of C atoms increased with the temperature.The relationship between the solubility of C atoms and the temperature in the melt of Cu and Sn is as follows: where x is the atomic fraction of C atoms dissolved in the melt, and T is the temperature of the melt.According to equations ( 2) and ( 3), the solubility of C atoms in Cu/Sn increased gradually with increasing  molten pool temperature.The C dissolved in melt would when the melt solidified, in the form of graphite or amorphous carbon.However, the hightemperature molten pool was approximately 10 6 °C/s during PBF-LB.In the rapid solidifying process, C atoms had negligible time to re-precipitate and remained solidly dissolved in the metal lattice in the form of interstitial atoms.

Thermal damage behaviour process of diamonds
A schematic of CuSn10-diamond composite by PBF-LB is shown in Figure 10.Diamonds were evenly distributed in the powder bed after powder-mixing in Figure 10(a).In the PBF-LB process, as the molten pool formed, diamonds were directly irradiated by the laser and part of diamond particle immersed in the high-temperature molten pool due to the low density of diamond, as shown in Figure 10(b).With the expansion of molten pool as shown in Figure 10(c), diamond particles migrated in the molten pool under the influence of the Marangoni effect and gravity (Long et al. 2020;Bouabbou and Vaudreuil 2022;AlMangour, Grzesiak, and Yang 2016).These particles were completely immersed in the high-temperature molten pool, thereby 'escaping' direct laser irradiation.Therefore, the thermal behaviour of diamond can be divided into two kinds: irradiation contact with laser beam (Figure 10 laser.As a continuous-wave laser applied in PBF-LB, when the laser reached the ablation threshold of diamond, the diamond would suffer permanent photo induced damage and therefore undergo phase transformation, as interaction type II reviewed in Introduction section.To evaluate the influence of continuous wave laser irradiation on the structural stability of diamond, the classic laser ablation theory was used in this study.The threshold of diamond can be expressed as (Jeschke and Garcia 2002;Li et al. 2020): where λ is the thermal conductive rate of the diamond A is the diamond absorption rate to laser, α is the thermal diffusivity of the diamond, t 0 is the laser dwelling time, T c is the crucial temperature and T 0 is the ambient temperature.The diamond particle size is 90 μm.Subsequently, t 0 is given by t 0 = d/v, where v is the scanning speed.
The lowest ablation threshold of diamond is approximately 1.21 × 10 7 W/cm 2 under direct laser irradiation at a wavelength of 1064 nm.To evaluate whether the laser fluence can affect the photo induced damage of the diamond, the equivalent laser fluence F laser used in this study can be expressed as (Li et al. 2020): where P is the laser power, t is the ablated duration, r is the laser spot radius, and v is the scanning speed.Calculations revealed that the maximum equivalent laser fluence was approximately 6.24 × 10 6 W/cm 2 in this experiment, which is one order of magnitude below the ablation threshold of diamond.Therefore, direct laser irradiation cannot induce the thermal damage of diamond during PBF-LB.As shown in Figure 10(c), several diamond particles were completely immersed in the high-temperature molten pool owing to the Marangoni effect and gravity.The contact between the particle surface and molten pool would be affected by the local high temperature.When the temperature was higher than the graphitisation temperature of diamond, the graphitisation transition occurred.In general, graphitisation occurred in an inert gas atmosphere at 1500°C (Iravani et al. 2012).According to Table 2 and Figure 6, sample No. 5 had a local graphitisation at the temperature of 1491.6°C.Below this temperature, diamond could avoid the thermal influence of the high molten pool temperature.
Under ambient conditions, the Gibbs free energy of diamond is 2.9 kJ, whereas it is zero for graphite; consequently, graphite is the stable phase.The Gibbs free energy change of diamond graphitisation under ambient conditions can be obtained according to Formula 6: where G graphite is Gibbs free energy of the graphite, G diamond is Gibbs free energy of the diamond.The fact that DG is less than 0 proves that diamond tends to change into graphite under ambient conditions.However, diamond exists under ambient conditions, owing to the high activation free energy barrier DG a (Wang, Scandolo, and Car 2005).Consequently, only when the free energy of the C of diamond is higher than DG a , the graphitisation transformation of diamond occurs.The transformation rate can be expressed based on the equation: where A is Arrheniusconstant, T is temperature.The transformation rate increased gradually with increasing temperature, which further verified the results of the I D :I G in the Raman spectrum, as shown in Figures 8(d,f).

Wear properties
According to the wear test results in Figure 11, the friction coefficients of the composites prepared at 1242.1°C and 1539.4°Cremained at 0.62 and 0.55, respectively.While the friction coefficients of the composites prepared at 1891.1°C fluctuated significantly and presented a gradual upward trend.The friction coefficient is small; the cutting obstacle is small, and the wear resistance is good (Yin et al. 2021).From Figure 11(b), with increasing graphitisation degree, the wear mark depth gradually increased and had values of 97.16, 116.15 and 118.29 μm.Therefore, with increasing degree of graphitisation, the wear properties of the composite became worse.
The worn surfaces morphologies of composite are shown in Figure 12.The worn surface morphology of the composites prepared by the lowest temperature of 1080°C (P = 120 W, v = 1100 mm/s) was shown in Figure 12(a).Although the diamond had no thermal damage under such conditions, due to insufficient melting of CuSn10 powder, there were many defects at the interface with poor retention force on diamond abrasives.The abrasives were easy to peel off during grinding, thus forming peeling pits and wide grooves.Figure 12(b) shows the worn surfaces morphology of the composite prepared at 1242.1°C and the wear mechanism was typical abrasive wear.At this temperature, no graphitisation of the diamond abrasives happened and the interface exhibited metallurgical bonding with good retention force.As the temperature of the diamond increasing to 1491.6°C, graphitisation occurred and the wear resistance of the composite decreased.The wear mechanism changed to adhesive wear with partially abrasive wear, as shown in Figure 12(c).When the temperature increased to 1891.1°C, with graphitisation of diamond aggravated, most of the diamond abrasives exhibited cleavage fracture and the fragments of the fracture diamond participated in the friction process, resulting in the three-body abrasion, leading to violent fluctuation of the friction coefficient, as shown in Figures 11(a) and 12(d) (Mandal et al. 2020).

Quantitative relationship
Table 3 shows the quantitative relationship of the 'PBF-LB parameters-Temperature-Graphitization degree- Wear resistance'.It can be seen that with the increase of the highest temperature of diamond, the graphitisation degree, bonding state, wear mechanism and wear mass loss all changed regularly and were correlated with each other.According to the temperature, the samples can be divided to four categories: . 1080.0°C.When the temperature was 1080°C, although graphitisation did not occur, the interface bond state was poor, and the diamond was easy to fall off during the friction process. .1192.9∼ 1420.1°C.As the temperature increased, the bonding state between diamond and CuSn10 was improved, which also improve the wear resistance of CuSn10-diamond composite samples, especially when the temperatures were 1192.9,1242.1 and 1248.7°C, the rate of wear mass loss was only 0.002-0.003. .1491.6 ∼1585.3°C.When the temperature reached 1491.6°C, the graphitisation occurred, and the wear mechanism changed into adhesive wear and abrasive wear.When the temperature is 1491.6∼1585.3°C, the degree of degree of graphitisation, adhesive wear and the rate of wear mass loss also increased with the further increase of temperature. .1676.5 ∼1896.1°C.When the temperature was 1676.5∼1896.1°C, the degree of graphitisation of diamond was further intensified and the cleavage fracture occurred.Meanwhile, the retention force of the CuSn10 on diamond deteriorated seriously, and the wear mechanism changed into three-body abrasion, and the wear resistance decreased greatly.
The establishment of the quantitative relationship provides a processing window for the fabrication of the CuSn10-diamond composites and the protection of diamond during PBF-LB.In addition, the method of establishing the quantitative relationship can be used in the fabrication of diamond composites by any highenergy beam additive manufacturing technology which can form high-temperature molten pools.

Conclusion
In the process of LAM of diamond tools, diamond and powder material parameters and laser process parameters are the main factors affecting the quality of their forming.With excellent thermal conductivity, the diamond will change the local thermal conduction ability of the alloy melt and the temperature distribution, which will affect the melt pool morphology, the microstructure near the diamond and the forming quality.Moreover, due to the thermal instability of diamond, the thermal damage such as oxidation, graphitisation and ablation, are likely to occur when diamond contact with high temperature molten pool.Therefore, it is extremely important to establish a quantitative framework to accurately evaluate the thermal damage behaviour of diamond abrasives and the relevant microstructure-performance characteristics, which can provide the basic support for relationship among process parameters and forming.In this study, by investigating the thermal evolution of the CuSn10-diamond composite by PBF-LB, the essential relationship among processing parameters, thermal behaviour of diamond abrasives, interfacial bonding and wear properties was quantitively revealed.The main findings are summarised as follows: (1) The CuSn10-Diamond composites were fabricated by PBF-LB.The thermal evolution of diamond particles in PBF-LB was obtained by simulation.The temperature of diamond presented two peaks in the process of molten pool moving forward,

Figure 4 .
Figure 4. Maximum temperature versus time curves of the diamond particle obtained with different processes: laser power (a) 120 W; (b) 140 W; (c) 160 W; (d)180 W.

Figure 6 .
Figure 6.SEM images of the microstructures of diamond particles with different PBF-LB parameters: No damage light damage and severe damage area correspond to the purple Area 1, the green Area 2 and the red Area 3.

Figure 7 .
Figure 7. XRD pattern of CuSn10-diamond composite samples with different diamond temperature.
Figure 10.Schematics of CuSn10-diamond composites produced via PBF-LB (a) mixed powders bed; (b) irradiation contact with laser beam; (c) thermal contact with the molten pool.

Figure 11 .
Figure 11.(a) The friction coefficient-time curve and (b) profile of the wear depth.

Table 2 .
Numerical simulation results of diamond peak temperature under different processing conditions.