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The microstructure design strategy is introduced to improve the mechanical property of a novel γ-Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB2 metal matrix composite (MMC) fabricated by hot isostatic press (HIP). With increasing the content of TiB2 from 0 to 3 wt%, the average grain size, {001} maximum texture index and average schmid factor of HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB2 parts generally decrease from 27.4 μm, 7.9 and 0.43 to 22.7 μm, 4.1 and 0.38, in addition, the crystallographic texture transforms from the mixture of (001) and (111) orientations to a strong (101) orientation. The phases evolution mechanism in the HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB2 parts can be divided into four steps: first of all, β phase transforms to γ and α phases, then, a small amount of new phases of TiB and TiC emerge by the diffusion of Ti and C atoms, subsequently, the β and α orderly transform to B2 and α2, lastly, the B2, α2, TiB2, TiB and TiC uniformly distribute in the γ matrix. Both the tensile strength and strain of HIP-processed Ti-43.5Al-6.5Nb-1.5Cr-0.5C/TiB2 components increase from 471.9 MPa and 1.7% to 653.4 MPa 2.1% with the increase of TiB2 content from 0 to 3 wt%. Keywords: Hot isostatic press, γ-TiAl/TiB2 MMC, Mechanical properties, EBSD, HRTEM

One of the first attempts on fabricating functionally graded materials (FGMs) of titanium/hydroxyapatite (Ti/HA) with quasi-continuous ratios by selective laser melting (SLM) was done. HA ratios varied among the layers of FGMs from 0 wt% to 5 wt% with 1 wt% gradient. The 3D reconstruction of Ti/HA FGM bulk with micro-pores was presented through micro-CT, and the percentage of micro-pore increased from 0.01% to 3.18% with the increasing of HA ratio. The scanning electronic microscope results showed that the crack was positively correlated to HA ratio with the crack density increasing from 1.5 × 10−4 μm/μm2 to 2.7 × 10−3 μm/μm2. The microstructure evolution from 0% to 5% HA ratios could be elucidated as long lath-shaped grains → long acicular-shaped grains → short acicular-shaped grains → continuous circle-shaped grains → quasi-continuous circle-shaped grains, due to the perturbation in the melting pool and obstruction of crystal development by HA. Accordingly, the FGM provides a wide range of nanohardness from 5.11 to 8.36 GPa and Vickers hardness from 3.42 to 5.67 GPa. Moreover, the fracture toughness from 2% to 5% HA ratios ranges from 3.41 MPa m1/2 to 0.88 MPa m1/2, which can be tailored to fit that of cortical and cancellous bones. Keywords: Metal-ceramic gradient materials, Titanium/hydroxyapatite, Selective laser melting, Interface, Fracture toughness

Ti-Nb alloys were in-situ fabricated by selective laser melting (SLM) to study the effect of Nb content on their phase transformation, microstructure evolution, mechanical properties and in vitro apatite-forming capability. Results show that α' martensite and β (Ti, Nb) phase are obtained in SLM-processed Ti-Nb alloys. The increase of Nb content results in the increase of β phase amount but decrease of β grain dimension. The former effect is due to the suppression of martensitic transformation and strengthening of solid solution behavior, while the latter phenomenon can be attributed to the increase of heterogeneous nucleation sites. The Ti-25Nb alloy possesses the lowest modulus of 18.7±1.4GPa due to the maximum content of β phase. The SLM-processed Ti-45Nb alloy exhibits superior strength of 1030±40MPa and microhardness of 356±7HV0.1, which is 97.32% and 52.53% higher than cast ones, respectively. The in vitro apatite-forming capability of Ti-25Nb alloy is the most superior compared to other Ti-Nb alloys. It demonstrates that β phase has the ability to induce apatite formation. The research shows that SLM could be used for in-situ fabrication of Ti-Nb bone implants with tailored mechanical and biomedical properties by adjusting Nb addition. Keywords: Ti-Nb alloy, Selective laser melting, Nb content, Mechanical property, In vitro apatite-forming capability

In this work, a novel approach combining liquid deposition with selective laser melting (SLM) is used for fabricating reduced graphene oxide (RGO)/S136 metal matrix composites (MMCs). The grain sizes, crystallographic textures, phase compositions and mechanical properties can be tailored by controlling the RGO content in the RGO/S136 MMCs. The results show that the average grain size reaches its smallest size of 0.75 μm when 0.1 wt% RGO was added to the RGO/S136 MMCs. As the RGO content is increased from 0 wt% to 0.5 wt%, a continuous transition of the grains from the (001) orientation to the (101) and (111) orientations is observed. In addition, the cellular dendritic grains transform into equiaxed fine grains with increasing RGO content. The SLM-prepared RGO/S136 MMCs are dominated by high-angle grain boundaries (˃15°) and the martensite (bcc) phase. The hardness, ultimate tensile strength and yield strength of the SLM RGO/S136 MMCs exhibit trends that initially increase and then decrease, with maximum values of 580.6 HV, 535.3 MPa and 515.8 MPa, respectively. This paper highlights the possibility of controlling the RGO content to achieve the desired microstructural characteristics and mechanical properties of RGO/S136 MMCs fabricated by the SLM process. Keywords: Selective laser melting, S136 steel, Reduced graphene oxide (RGO), Microstructure, Mechanical properties

This work presents a comprehensive study of the densification behavior, phase and microstructure development, high temperature tensile performance of a novel near-α high-temperature titanium alloy fabricated by hot isostatic pressing (HIP) at representative temperatures. The results indicated that numerous rod-like S2 silicides ((TiZr0.3)6Si3) and α2 phase (Ti3Al) precipitated from α matrix. The microstructural characteristics of HIP-fabricated parts experienced a successive change on increasing the HIP temperature: lathlike structure + little equiaxed grains → equiaxed grains + little lathlike structure → fully equiaxed grains. In addition, the grain size of samples unceasingly growed up with the increase of HIP temperatures. Over the entire tensile tests temperature range, the equiaxed grains plus little lath-like structure (HIP-B) exhibited the highest tensile strength. As to the ductility, the elongation of specimens increased successively with the increase of HIP temperatures, which is mainly due to the type of microstructure and the diffusion-metallurgical bond. Keywords: Near-α high-temperature titanium alloy, Hot isostatic pressing (HIP), Silicide, Microstructure evolution, High tensile properties

A novel titanium alloy (Ti–5.5Al–3.4Sn–3.0Zr–0.7Mo–0.3Si–0.4Nb–0.35Ta) with a relative density of 99.34% was produced by selective laser melting (SLM) under the condition of 140 W laser power and 400 mm/s scanning speed. The microstructure, high temperature oxidation resistance and micro-hardness were studied. The results showed that the acicular martensitic α′ phase was about 0.5 μm in width due to the high cooling rate during the SLM process. The comparative measurements showed that the as-SLMed sample had higher oxidation resistance and micro-hardness than those of the as-casted one. And the oxidation mechanism was proposed. Keywords: Selective laser melting, Titanium alloys, Microstructure, High temperature oxidation resistance

Biomimetic functionalization is a pressing need for orthopedic implants to achieve reinforced osseointegration and accelerated osteogenesis, thereby obtaining a successful clinical outcome. To realize bioactivity, Ti Nb alloys with varying Nb contents (0–45 at.%) were additively manufactured using elemental powder blends. The regulation of the Nb contents could balance the surface constituent ratio of Nb2O5 and TiO2, enhancing the formation of the hydroxyl group and surface hydrophilicity. Moreover, the effect mechanism of Nb2O5 on immune modulation and bone regeneration was first put forward. The incorporation of Nb improved the viability of macrophages by inducing a macrophage polarization toward an anti-inflammatory M2-like state. The variation of morphological and up-regulated expression of anti-inflammatory factors led to a more favorable osteoimmune microenvironment for osteogenesis, promoting the osteogenic differentiation of osteoblasts in vitro. Considering the surface constituent and in vitro biological performance, 3D-printed Ti 25Nb scaffolds were placed into the femoral condyle of the rabbit. The Micro-CT and histological analysis indicated that Ti 25Nb scaffolds could accelerate bone regeneration and reinforce bone integration as relative to pure Ti. Overall, the Ti 25Nb scaffold exhibited structural bionic ability, surprising immunomodulatory properties, superior bone regeneration and osseointegration capacity, showing exceptional potential in the treatment of bone defects.

Using numerical simulations and experimental tests, the temperature and velocity fields of the molten pool during selective laser melting (SLM) were investigated, where the laser scanning speed ranging from 2.5 m/s to 0.3 m/s was employed. Experiments for single tracks and part samples were conducted for verification. Three kinds of molten pool states were identified and investigated: unstable state, transition state and stable state. The unstable state is characterized by numerous balling defects, where the bulk density is severely deteriorated. The transition state is featured by the transition region where the melt velocity is relatively lower, and the molten pool is vulnerable to the necking defect. The molten pool with a depression region is identified as the stable state. A small depression is favorable for improving the surface quality of single track and the bulk density. However, exorbitant energy input will convert the depression into a keyhole. Additionally, a threshold of the scanning speed was found, where the bulk density peaked. Over the threshold, the density decreased continuously with the speed increasing. However, the density slightly decreased by 1.5% when the speed was below the threshold; this anomaly was ascribed to the residual pores induced by the recoil pressure. Keywords: Scanning speed, Selective laser melting, Temperature and velocity fields, Molten pool states, Threshold

The use of porous structures is gaining popularity in biomedical implant manufacture fields due to its ability to promote increased osseointegration and cell proliferation. Selective laser melting (SLM) is a metal additive manufacturing (MAM) technique capable of producing the porous structure. Adjusting the parameter of scan line spacing is a simple and fast way to gain porous structures in SLM process. By using the medical alloy of Ti6Al4V, we systematically study the influence of the scan line spacing on pore characteristics and mechanical properties of porous implant for the first time. The scanning electron microscope (SEM) results show that the porous Ti6Al4V implants with interconnected pore sizes which ranges from 250 to 450 μm is appropriate for compact bone. The compression strength and modulus of the porous Ti6Al4V implants decrease with the increase of the scan line spacing, and two equations by fitting the data have been established to predict their compression properties. The compressive deformation of the porous Ti6Al4V implants presented an adiabatic shear band (ASB) fracture, which is similar to dense Ti6Al4V owing to the dense thin wall structures. The ability to create both high porosity and strong mechanical properties implants opens a new avenue for fabricating porous implants which is used for load-bearing bone defect repair and regeneration.