To fabricate metallic 316L/HA (hydroxyapatite) materials which meet the requirements of an implant's mechanical properties and bioactivity for its function as human bone replacement, selective laser melting (SLM) has been employed in this study to prepare a 316L stainless steel matrix, which was subsequently covered with a hydroxyapatite (HA) coating using the sol-gel method. High density (98.9%) as-printed parts were prepared using a laser power of 230 W and a scanning speed of 800 mm/s. Austenite and residual acicular ferrite existed in the microstructure of the as-printed 316L stainless steel, and the sub-grain was uniform, whose primary dendrite spacing was around 0.35 µm. The as-printed 316L stainless steel showed the highest Vickers hardness, elastic modulus, and tensile strength at~(~means about; same applies below unless stated otherwise) 247 HV,~214.2 GPa, and~730 MPa, respectively. The elongation corresponding to the highest tensile strength was~38.8%. The 316L/HA structure, measured by the Relative Growth Rate (RGR) value, exhibited no cell cytotoxicity, and presented better biocompatibility than the uncoated as-printed and as-cast 316L samples.implants to replace shoulders, knees, and other body parts of the human being [7-9]. However, it is difficult to induce good attachment and growth of bone cells from 316L stainless steel and it also has no bioactive capabilities, which increases the likelihood for it to lead to loosening of the implant and premature failure [10][11][12]. The HA coating, however, is likely to provide excellent bioactivity and biocompatibility to metallic implants [13][14][15].For individual patients, mass-produced implants may not completely fulfill their needs. Customized implants, with geometry deriving from their own magnetic resonance imaging (MRI) data, are urgently needed [16]. SLM, which is a powder-bed-based additive manufacturing technology, can be used to selectively melt metal powders layer by layer through a highly focused and computer-controlled laser beam [17,18]. It has been used to successfully prepare many kinds of metallic biomaterials, such as stainless steel, alloys of titanium, magnesium, and medical noble metals, and compared with some of the more traditional approaches, it provides superior mechanical properties and a relatively simpler manufacturing process [19,20].In retrospect, some studies around SLM-processed 316L stainless steel with different laser parameters and lattice structure designs have been undertaken [21][22][23]. In order to testify its feasibility as an implant, simple cytotoxicity and biocompatibility tests were conducted while comparing different manufacturing and post-processing methods [24][25][26][27][28]. However, these can hardly solve the problem of poor bioactivity, and may even cause a failure of metallic implants. As a time-honored bio ceramic which realizes higher osteoblast activity, HA material is currently quite popular for its special applications in regenerative implants and bone void fillers [29]. Metallic implants, with ...

The determination of microstructural details for powder materials is vital for facilitating their selective laser melting (SLM) process. Four widely used steels (316L, H13, P20 and 18Ni300) have been investigated to detail their powders’ microstructures as well as laser absorptivity to understand their SLM processing from raw material perspective. Phase components of these four steel powders were characterized by X-ray diffraction (XRD), synchrotron radiation X-ray diffraction (SR-XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to reveal the surface structure of these four steel powders. It is found that phase components of H13, P20 and 18Ni300 are mainly composed of martensite and a small amount of austenite due to the high cooling rate during gas atomization processing, while 316L is characterized by austenite. XPS results show that the four steel powders all possess a layered surface structure, consisting of a thin iron oxide layer at the outmost surface and metal matrix at the inner surface. It is found that the presence of such oxide layer can improve the absorptivity of steel powders and is beneficial for their SLM process.

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Cu and Cu alloys are important materials with extensive industrial applications in fields such as electronics, construction, and transportation. [1] Tin bronze (Cu-Sn) was one of the earliest alloys used by humans, [2,3] and offers outstanding wear and corrosion resistance. It is widely employed in the marine industry, [4,5] and as a bearing material. [6] Cu-Sn alloys are also used in electrical connectors and electronic components due to their good machinability. [7] Phosphorus (P) is commonly used as an alloying element in Cu-Sn alloys at doping levels of up to 0.5 wt%, and offers various beneficial effects at optimal concentrations. [8][9][10][11] Specifically, P doping can potentially lead to a lower stacking fault energy for an easier plastic deformation, [8] an enhanced wear resistance due to grain boundary phase formation to refine grain size, [9] an improved melt property due to lower viscosity, [10] and purified melt due to oxygen scavenging from the Cu matrix. [10,11] In contrast, Cu-Sn alloys with a Sn content above 5 wt% tend to generate a brittle δ phase within the microstructure, which lowers the plasticity. Thus, casting has become the most popular fabrication technique for high-Sn-Cu alloys (e.g., Cu-10Sn). [11] However, as-cast Cu-10Sn is prone to defects such as low densification, shrinkage cavities, microcracks, and severe segregation, thus advanced manufacturing processes are required. [12,13] Alternatively, recently developed laser-based additive manufacturing (AM) and 3D printing techniques can be used for the manufacturing of Cu-Sn alloys. They offer several advantages, including free-form fabrication without molds, friendly working environment, and short production cycles. [14][15][16] Many studies have investigated the production of high-quality parts from various materials using AM. However, Cu and Cu alloys are often regarded as highly reflective materials, particularly for near-infrared (NIR) laser beams, which can result in poor laser absorptivity. [17][18][19][20][21][22] Gu et al. [23] used selective laser sintering (SLS) to print Cu-10Sn and Cu-8.4 P components, whereas Mao et al. [13] used selective laser melting (SLM) to manufacture Cu-15Sn parts with a relative density of 99.6% at a laser power of 187 W, scanning speed of 185 mm s À1 , and 0.17 mm of hatch space. Furthermore, a bimetallic structure consisting of 316L stainless steel and Cu-10Sn was produced using SLM. [24,25] SLS and SLM are laser-based AM technologies, whereas selective electron beam melting (SEBM) uses an electron beam as the heat source to melt the feedstock powder to overcome the poor laser absorptivity of many Cu and Cu alloys. [26] However, SEBM normally has a lower forming accuracy and surface roughness than SLM. [14,15,26] Overall, currently SLM offers several advantages, but SLM-prepared Cu and Cu alloys (e.g., Cu-10Sn) can also

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