Within the realm of metal additive manufacturing, laser powder bed fusion (PBF-LB) has maintained a dominant role by offering exceptional geometric freedom, fine feature resolution and fine ...microstructure features. However, low productivity still presents a bottleneck in the adaptation of PBF-LB in most industrial contexts. In recent literature, build-up rates have shown to improve notably when thicker powder layers are employed. However, systematic analyses linking processing parameters, productivity, microstructural state and mechanical properties are lacking. This study aims to fill this gap for Ti6Al4V alloy with powder layer thicknesses in the range of 60 µm to 300 µm, specifically using system-agnostic process parameters applicable to the majority of currently available commercial AM systems. The results revealed that Youngs modulus (∼110 GPa) and yield strength (∼1.1 GPa) remain comparable to ‘conventional’ PBF-LB Ti6Al4V throughout the investigated range of layer thickness. At the same time elongation to failure decreases from 11.4 ± 2.7% at 60 µm to 8.4 ± 1.1% at 180 µm and finally to 2.0 ± 0.3% at 300 µm, which was microscopically correlated with increased occurrence of lack-of-fusion porosity in layers exceeding 180um. It was also demonstrated that the changes in the parent β phase texture arising from process changes could have contributed to decreased ductility at thicker layers. Ultimately, while productivity increases with layer thickness up to 8.76 mm3/s at 300 µm, the achievable build rate appears to plateau around 300 µm layer height and require further expansion of the laser power characteristics to enable additional gains without compromising mechanical performance.
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•Productivity and performance of PBF-LB Ti6Al4V with 60 - 300 μm powder layer thickness were systematically explored.•In contrast to volumetric energy density, a machine- and material- agnostic Fourier number approach was employed.•With increased layer thickness, ductility was adversely affected by gradually increased porosity and prior-β texture changes.•Productivity gains stagnated for 240 - 300μm layer thicknesses due to limited power (400 W) of conventional PBF-LB systems.
In this paper, the recent progress on Ti6Al4V fabricated by three mostly developed additive manufacturing (AM) techniques-directed energy deposition (DED), selective laser melting (SLM) and electron ...beam melting (EBM)-is thoroughly investigated and compared. Fundamental knowledge is provided for the creation of links between processing parameters, resultant microstructures and associated mechanical properties. Room temperature tensile and fatigue properties are also reviewed and compared to traditionally manufactured Ti6Al4V parts. The presence of defects in as-built AM Ti6Al4V components and the influences of these defects on mechanical performances are also critically discussed.
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•Recent progresses in additively manufactured Ti6Al4V were reviewed.•Laser direct deposition, selective laser melting and electron beam melting were comparatively studied.•Processing-microstructure-tensile and fatigue properties relationship were established.•Effects of defects on mechanical properties were also addressed.
We elucidate the effect of nano-SiC whisker (SiCw) on the microstructure and mechanical properties of Ti6Al4V alloy manufactured by selective laser melting (SLM). The transformation of ...cross-sectional plate-like α grains and longitudinal-sectional β columnar grains to equiaxed grains could be achieved by adding a trace amount of SiCw, and the weak texture strength microstructure with fine equiaxed grains was obtained. The in situ formed nanosized TiC particles promoted grain refinement through three mechanisms: (i) The diffusion distribution of nanosized TiC particles provided a favorable nucleation position for the α phase, it also limited the growth of the α phase. (ii) Nanosized TiC particles were dispersed to fix dislocations and grain boundaries, inhibit the grain growth. (iii) Nanosized TiC was embedded in the matrix and bound well to the matrix. The Ti matrix was easy to nucleate on some specific crystal planes of primary TiC, which increased the nucleation rate. In addition, the addition of SiCw significantly improved the mechanical properties of Ti6Al4V alloy, compared with that of the Ti6Al4V alloy (360.2 HV), the microhardness of the sample with 1.0-wt% SiCw (522.7 HV) increased by 45.1%. The addition of 0.5-wt% SiCw (1445.34 MPa) increased the ultimate tensile strength by 19.4% compared with that of the Ti6Al4V alloy (1210.13 MPa), and good ductility was maintained. The results show that the microstructure of Ti6Al4V alloy can be significantly improved by adding a trace amount of SiCw, which provided an effective way for the grain refinement of titanium matrix composites manufactured by SLM.
In this paper, the Ti6Al4V alloy surface was modified via ceramic conversion treatment (CCT) with or without a pre-deposited silver layer. After characterizing the surface morphologies, ...microstructure and phase constituents of the ceramic oxide layer formed at 620 °C, we investigated the surface hardness and the cross-sectional nano-hardness profile under the oxide layer. The static load-bearing capacity of the oxide layers was examined by applying discrete loads via a Vickers indenter and observing the indentations. A scratch test was used to evaluate the load-bearing capacity and the adhesion/cohesion of the oxide layers. The wettability of the surface changed due to the incorporation of silver and the change of surface morphology. Reciprocating friction and wear test was used to assess the tribological properties. Small and dispersed silver nanoparticles and clusters were found in the oxide layer of the Ag pre-deposited Ti6Al4V samples, and they had much better tribological properties in terms of reduced coefficient of friction and wear volume. With the assistance of silver, the efficiency of the CCT was significantly improved.
Powder bed fusion (PBF), including selective laser melting and electron beam melting, fabricates complex, porous, osseointegrative implants for widespread clinical use. Fatigue testing is imperative ...for predicting long-term strength and durability of rough and surface porous implants while bone remodels around and grows into the implant. This study analyzes different materials (Ti6Al4V and Co28Cr6Mo) with varying topographies including as-printed surface roughness and the addition of a surface porous layer common to implants. The results are compared to wrought and PBF controls that are polished and machined. Moreover, different PBF techniques for titanium result in different as-printed surface roughness (∼0.07–17 μm) and microstructure. The fatigue data demonstrates that the surface finish impact was stronger in Ti6Al4V versus CoCr and SLM Ti6Al4V HIP + surface porous gyroid samples didn't perform worse than the roughest solid sample without surface porosity (EBM Ti6Al4V). With the same mechanical surface finishes, the SLM and wrought Ti6Al4V samples display similar fatigue resistance (800 and 850 MPa respectively), while EBM samples remain inferior (350 MPa). This study provides a foundation to compare fatigue resistance across materials and surface topographies through different fabrication techniques to optimize the lifespan of orthopedic implants while incorporating rough as printed surfaces and added surface porosity, both of which are essential for osseointegration.
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•This study systematically tested the effect of material, manufacturing technique, and surface topography (surface finish and porosity) on fatigue life.•Distinct microstructures were found amongst the samples generated with different manufacturing techniques.•A critical surface roughness of ∼0.2 μm was found in which further reducing the surface roughness was relatively ineffective in increasing fatigue strength.•Increasing gyroid thickness onto the surface of a SLM Ti6Al4V HIP sample had limited additional impact on decreasing fatigue strength.
The paper presents the optimization of the sintering process by SPS of Ti6Al4V powders and the study of the impact of graphene oxide (GO) on this material. The effect of the addition of graphene ...oxide (GO) on Ti6Al4V was determined. Optimization of the mixing process was performed for the Ti6Al4V - xGO system. On the basis of the homogeneity of the carbon distribution, determined by X-ray spectrometry (EDS energy dispersion spectroscopy), the optimal mixing parameters were selected. In order to identify the phase boundaries between Ti6Al4V and GO, tests were performed using SEM, TEM and Raman spectrometry techniques. The appropriate selection of the parameters of the mixing and sintering process made it possible to obtain dense Ti6Al4V-GO sinters, which confirms that the addition of GO strengthens Ti6Al4V and the proposed method is an effective method of strengthening the Ti6Al4V alloy.
•The presence of GO flakes in the sintered material causes a local grain size reduction around GO.•Extending the mixing time affects the GO reduction process.•The addition of single-layer GO results in obtaining the Ti6Al4V-GO sinter with the highest hardness.
•Sub-spherical pores form in the interlayer region of LMDed TiCp/Ti6Al4V composite.•Synchronized UIT is effective in reducing defects and porosity.•UIT affects the elimination of pores through defect ...nucleation and melt pool flow.
TiCp/Ti6Al4V composites produced by laser metal deposition (LMD) are usually characterized by internal defects and resultant deteriorated mechanical properties. In the present work, a synchronous ultrasonic impact treatment (UIT) was introduced during LMD of TiCp/Ti6Al4V composites. The effect of synchronous UIT on the defects was investigated. The defects in the LMDed composites are sub-spherical pores distributed in the interlayer region. With the assistance of UIT, the maximum surface height difference reduces from 200.2 ± 0.5 μm to 25 ± 0.5 μm and the internal porosity decreases from 1.95% to 0.09%, which is attributed to inhibiting the nucleation of defects and increasing molten pool flow. This work may provide a solution to effectively reduce the defects in additively manufactured parts.
The strength and energy absorption properties of the auxetic 3D anti-tetrachiral (3ATC) lattice, a member of the newly formalized joint-rotation-dominated cellular topology, were studied for the ...first time, using analytical modelling, simulations and experiments employing additively manufactured titanium alloy (Ti6Al4V) lattices. A limited ductility failure model was employed in the simulations to accurately account for the enhanced brittleness of 3D printed Ti6Al4V. The 3ATC lattices exhibited 2 distinct relative strength vs. relative density relationships. If the relative density was varied through changes in strut length, the relationship was linear, a result that has, until now, been a distinguishing trait of rigid stretch-dominated lattices, rather than auxetic lattices, which normally experience strut bending. On the other hand, if the relative density was varied through changes in strut width, the relationship was highly nonlinear and does not follow the power law trend that is typical of many cellular solids. The strength of 3ATC lattices can be higher than that of stochastic foams, but were lower than those of stretch-dominated designs. In addition, 3ATC bulk lattices exhibited highly uniform properties across the three different orthogonal loading directions, despite individual unit cells being highly orthotropic. The failure of 3ATC lattices was characterized by a series of bumps in the plateau regime, which corresponded to the sequential failure and compaction of individual unit cell layers in the lattice. The specific energy absorbed during the failure process was found to be linearly related to the failure strength. The mechanical characteristics of the 3ATC lattices are dependent on 3 normalized design parameters: i) strut length, ii) strut width, and iii) eccentricity, offering enhanced flexibility for design optimization over conventional lattice designs. When manufactured with a material of high specific strength like Ti6Al4V, it was shown that 3ATC lattices can be useful as lightweight and high strength auxetic architected metamaterials that provide good energy absorption capabilities.
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•Strength and plastic deformation of rotation-dominated 3D Anti-Tetrachiral (3ATC) structures investigated in detail for the first time.•2 distinct relative strength vs. relative density relationships – one is linear, like the ‘stretch-dominated’ topology, another highly nonlinear and does not follow conventional power law.•Properties were symmetric in the X, Y and Z axes for large lattices but anisotropic for unit cells i.e. Properties becomes increasingly isotropic with more unit cells in lattice.•Relative strength for rotation-dominated lattices can be better than bending-dominated structures but were generally lower than stretch-dominated geometries. When fabricated with Ti6Al4V, high specific strengths, as well as good specific energy absorption and energy absorption efficiencies, were observed.•Finite element modelling indicates that the additively manufactured Ti6Al4V had limited ductility and was inherently brittle to some extent.
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