Ti6Al4V Powder Research Articles

Influence of Powder Morphology and Microstructure on the Cold Spray and Mechanical Properties of Ti6Al4V Coatings

The powder microstructure and morphology has significant influence on the cold sprayability of Ti6Al4V coatings. Here, we compare the cold sprayability and properties of coatings obtained from Ti6Al4V powders of spherical morphology (SM) manufactured using plasma gas atomization and irregular morphology (IM) manufactured using the Armstrong process. Coatings deposited using IM powders had negligible porosity and better properties compared to coatings deposited using SM powders due to higher particle impact velocities, porous surface morphology and more deformable microstructure. To evaluate the cohesive strength, multi-scale indentation was performed and hardness loss parameter was calculated. Coatings deposited using SM powders exhibited poor cohesive strength compared to coatings deposited using IM powders. Images of the residual indents showed de-bonding and sliding of adjacent splats in the coatings deposited using SM powders irrespective of the load. Coatings deposited using IM powders showed no evidence of de-bonding at low loads. At high loads, splat de-bonding was observed resulting in hardness loss despite negligible porosity. Thus, while the powders from Armstrong process lead to a significant improvement in sprayability and coating properties, further optimization of powder and cold spray process will be required as well as consideration of post-annealing treatments to obtain acceptable cohesive strength.

Manufacturability of Overhanging Holes Using Electron Beam Melting

This study aims to investigate the manufacturability of overhang round holes with and without support. The experiments were conducted by electron beam melting (EBM) using a Ti6Al4V powder. A large number of overhanging holes with and without support were fabricated and evaluated. The geometrical accuracy, mechanical properties, and microstructures were utilized as a measure of the process performance. It was demonstrated that overhanging features can be built successfully without support up to a certain dimension (or threshold value). Beyond that value, a minimal support structure can be employed to achieve the most suitable trade-off between production time, cost, and accuracy.

Parametric study and characterization of AlN-Ni-Ti6Al4V composite cladding on titanium alloy

Titanium and its alloys have wide applications in the field of aerospace as well as medical. But their poor surface properties (i.e. low hardness and wear resistance) restrict the uses in the harsh working environment. To address this drawback, a composite cladding of aluminum nitride (AlN), Nickel (Ni) and Ti6Al4V powders was formed on the Ti6Al4V plate. Three process parameters namely, laser power, scanning speed and percentage composition of AlN in the powder mixture were considered to study their influence for obtaining required hardness and layer thickness of the cladded surface. Further, characterization of clad layer morphology, micro-hardness in the subsurface layer, wear behavior of the cladded surface and elemental compound formations were carried out. The experiment investigation revealed that the micro-hardness of the cladded surface is in the range of 1000–1250 HV0.5kg which is approximately three times of the parent material. Also, very few pores and cracks were noticed on the cladded surface. It was observed that fine-grain columnar structure forms dendrite which enhances mechanical properties of the cladded surface. XRD result shows the good affinity between substrate material and powders and the formation of intermetallic compounds like TiN, Ni3Ti, and Ti3AlN which improve the micro-hardness properties of the cladded layer.

Dough Extrusion Forming of Titanium Alloys—Green Body Characteristics, Microstructure and Mechanical Properties

Titanium and its alloys are widely used in structural applications owing to superior mechanical properties and corrosion resistance. In the present study, a simple powder metallurgy-based process is developed to fabricate dense components through formation of dough under ambient condition using Ti6Al4V powder along with chitosan powder as dough forming additive and acetic acid as solvent. The prepared samples had ∼66±1.7% green density and 97.3±2.1% sintered density of the theoretical value. The microstructure of Ti6Al4V was investigated using scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) spectroscopy. Micro-CT analysis was carried out for distribution of defects and their influence on flexural strength and microhardness was assessed as well. The prepared green samples had uniform particle distribution that resulted in minimum deformation after sintering. Assessment of mechanical properties revealed that the values of hardness and flexural modulus for sintered samples were comparable to the reported values of Ti6Al4V components prepared using other process. Therefore, the developed method of dough forming for dense titanium components using powder metallurgy route is a simple and viable alternative.

Microstructure and properties of functionally graded materials Ti6Al4V/TiC fabricated by direct laser deposition

PurposeThis paper aims to manufacture Ti6Al4V/TiC functionally graded material (FGM) by direct laser deposition (DLD) using Ti6Al4V and TiC powder. The objective is to investigate the effect of process parameters and TiC composition on microstructure, Vickers hardness and mechanical properties.Design/methodology/approachPowder blends with three different volume percentages of Ti6Al4V and TiC were used as feed material for DLD process. Five experiments with different values of laser power and scan speed were conducted to investigate the effect on microstructure and Vickers hardness for different compositions of feed material. Mini-tensile tests were performed to evaluate the mechanical properties of the FGM samples. Digital image correlation (DIC) was applied to estimate Young’s modulus and ultimate tensile stress (UTS) of heterogeneous material.FindingsThis paper indicates that primary carbide, eutectic carbide and un-melted carbide phases are formed in the FGM deposit. As the energy density was increased, the primary and secondary dendrite arm spacing was found to increase. As TiC composition was increased, Young’s modulus increased and UTS decreased. The dendritic morphology of primary TiC growth was expected to cause low resistance for crack propagation, causing lower UTS values. Tensile specimens cut in vertical orientation were observed to possess higher values of Young’s modulus in comparison with specimens cut horizontally at low carbon content.Originality/valueCurrent work presents unique and original contributions from the study of miniature FGM tensile specimens using DIC method. It investigates the effect of specimen orientation and TiC content on Young’s modulus and UTS. The relationship between energy density and dendritic arm spacing was evaluated. The relationship between laser power and scan speed with microstructure and Vickers hardness was investigated.

Effect of Microwave Sintering Parameters on the Physical and Mechanical Properties of Pure Ti and Blended Elemental Ti Alloys

Microwave sintering (MWS) was used to consolidate hydride de-hydride Ti powder and blended elemental Ti6Al4V, Ti5Fe and Ti5Al5Mo5V3Cr (Ti5553) powder mixtures. The amount of powders used to prepare the powder compacts was scaled up to 500g.The effect of the MWS conditions on the relative density, porosity distribution, microstructure and tensile properties were studied. Furthermore, uniformity in distribution of the alloying elements was checked. For most of the materials considered, a combinations of sintering temperature of 1200oC and 1300oC and holding time of 5 to 30 min resulted in significantly improved density. Nevertheless sintering temperature of at least 1300oC was required for pore coalescence and high tensile properties.

Characteristics of Ti6Al4V Powders Recycled from Turnings via the HDH Technique

The objective of this research is for Ti6Al4V alloy turnings, generated during the machining of implants, to produce powders for the fabrication of Ti base coating via the cold spray method. In order to decrease the cost of powder production and increase the recycling rate of the turnings, the hydrogenation-dehydrogenation (HDH) process has been utilised. The HDH process consists of the following sequence: surface conditioning of the turnings, hydrogenation, ball milling (for powder production), and dehydrogenation. Afterwards, the properties of the recycled powder were analysed via phase, chemical, and morphological examinations, and size and flowability measurements. Usability of the powder in additive manufacturing applications has been evaluated via examining the characteristics of the deposit produced from this powder by the cold spray method. In short, promising results were obtained regarding the potential of the recycled powders in additive manufacturing after making minor adjustments in the HDH process.

Microstructural and property evolution of Ti6Al4V powders with the number of usage in additive manufacturing by electron beam melting

The influence of reused times on the characteristics and properties of Ti6Al4V (TC4) powder and resulting bulk materials were systematically investigated in additive manufacturing by electron beam melting (EBM). Optical microscope, X-ray diffraction and nano-indentation were used to characterize the powders. Optical microscope results indicated that the microstructure evolved from non-equilibrium to equilibrium state of α and β phase with increasing reuse times. The micro-hardness and Young’s modulus of reused powders were enhanced with the increase of reuse times. The tensile properties of bulk final product fabricated from the mixed powders were nearly equal or superior to that prepared by 100% fresh powder. In short, the mixing usage of initial and reused Ti6Al4V powders for additive manufacturing is acceptable.

Processing and properties of highly porous Ti6Al4V mimicking human bones

Abstract

Fabrication of porous metals layered by laser-assisted melting of sprayed Ti6Al4V powder and foaming agent mixture

This paper demonstrates the fabrication process of a porous metal using the direct energy deposition (DED) process, wherein Ti6Al4V powders mixed with a foaming agent (TiH2) were sprayed on the Ti6Al4V substrate, and subsequently, melted with the substrate using a high-power laser beam. Before the solidification of the molten metal, the hydrogen gas generated from TiH2 caused pores inside the deposited layer. The fabricated porous structures had porosities of 22% and 11% for laser powers of 900 and 1100 W, respectively, which indicated that the densities of the layered porous structures could be controlled by varying the process parameters. Finally, the compression testing of the samples proved that the porous structure fabricated by DED is significantly effective in absorbing mechanical energy.

Selective electrochemical machining of the steel molds in hot isostatic pressing of Ti6Al4V powder

ABSTRACTAnodic dissolution is proven to be an effective method to remove stainless steel molds from Ti6Al4V compacts obtained from powder by hot isostatic pressing. Two different working solutions were studied: 2 M NaCl and 2 M NaCl + 0.05 M Na2EDTA. While both were capable of removing the steel mold, the latter was also capable of removing the diffusional layer made by the intermetallic phases generated between titanium and steel during the compaction process.

Determination of melt pool dimensions using DOE-FEM and RSM with process window during SLM of Ti6Al4V powder

Selective laser melting (SLM) shows a positive prospect as an additive manufacturing (AM) technique for fabrication of 3D parts with complicated structures. A transient thermal model was developed by the finite element method (FEM) to simulate the thermal behavior for predicting the time evolution of temperature field and melt pool dimensions of Ti6Al4V powder during SLM. The FEM predictions were then compared with published experimental measurements and calculation results for model validation. This study applied the design of experiment (DOE) scheme together with the response surface method (RSM) to conduct the regression analysis based on four processing parameters (exactly, the laser power, scanning speed, preheating temperature and hatch space) for predicting the dimensions of the melt pool in SLM. The preliminary RSM results were used to quantify the effects of those parameters on the melt pool size. The process window was further implemented via two criteria of the width and depth of the molten pool to screen impractical conditions of four parameters for including the practical ranges of processing parameters. The FEM simulations confirmed the good accuracy of the critical RSM models in the predictions of melt pool dimensions for three typical SLM working scenarios.

Investigation on Ti6Al4V laser metal deposition using Taguchi based grey approach

An optimization of laser metal deposition process considering tensile strength, clad hardness, clad grain size and clad porosity as performance characteristics were investigated. The influence of laser power and laser scan speed on the thermal gradient and cooling rate with regard Ti6Al4V powder coating on Ti6Al4V substrate was focused. Taguchi’s experimental design approach is employed for planning the experiments and analyzing the dependency of input variables on desired performance measures such as micro hardness, tensile strength, porosity and grain size. The laser scan speed is found as the dominant factor on the clad hardness while laser power has the influencing effect on grain size of the substrate. GRA is opted for determining the multi performance machining characteristics of laser metal deposition process. The experimental outcomes reveal that the proposed method of multi objective optimization considerably enhances the multi performance machining characteristics.

Standard method for microCT-based additive manufacturing quality control 4: Metal powder analysis

X-ray micro computed tomography (microCT) can be applied to analyse powder feedstock used in additive manufacturing. In this paper, we demonstrate a dedicated workflow for this analysis method, specifically for Ti6Al4V powder typically used in commercial powder bed fusion (PBF) additive manufacturing (AM) systems. The methodology presented includes sample size requirements, scan conditions and settings, reconstruction and image analysis procedures. We envisage this method will support standardization in powder analysis in the additive manufacturing community. This is aimed at ultimately improving the quality of additively manufactured parts, through the identification of impurities and defects in powders.•MicroCT analysis of metal powders for additive manufacturing•Method describes a standard workflow simplifying usage of the technique•Sample requirements and image analysis workflow is described

Mechanical Properties of Porous Structures Produced by Selective Laser Melting of a Ti6Al4V Alloy Powder

The compression Young's modulus and strength of lattice structures with porosity between 47.8% and 82.6% produced by Selective Laser Melting (SLM) of a Ti6Al4V powder were investigated. The Young's ...

Processing Parameters Influence on Microhardness in Laser Metal Deposited Titanium Alloy using Design if Experiment

Laser Metal Deposition (LMD) is an additive manufacturing process for producing complex parts directly from the Computer Aided Design (CAD) model of the part and for repair of an existing worn out part. The LMD process is governed by processing parameters: laser power, gas flow rate, powder flow rate and scanning speed that influence the microhardness produced during the LMD process. In this study, statistical design of experiment to was employed to investigate the influence of processing parameters on the microhardness of laser metal deposited of Ti6Al4V powder on Ti6Al4V substrate. Full factorial design was used in this study because of its ability to capture the main effects and possible interaction effects of these processing parameters. Each processing parameters was set at low and high values and a total of sixteen (16) experiments was performed and the microhardness of each sample was measured and analyzed.

Parametric study of surface morphology for selective laser melting on Ti6Al4V powder bed with numerical and experimental methods

A three-dimensional (3D) selective laser melting (SLM) model comprising coupled heat transfer and flow behavior is proposed. The free surface of the melt pool is calculated by the volume-of-fluid (VOF) method, which is a means of acquiring the surface morphology. In this research, laser powers and laser scanning speeds were normalized to characterize the influence on the surface morphology. Results showed that when the scanning speed was increased, the surface morphology initially became flatter, but then roughness developed again at high speed case. Further, as the laser power was increased, the surface morphology gradually roughened. To better describe the surface-morphology phenomenon according to different laser parameters, the melt pool volume and melt pool lifetime were also investigated. With these two factors constrained, a fine surface could be obtained with a low melt pool volume and proper lifetime (approximately 100 to 130 μs). The surface morphology and the width of the melt track were experimentally acquired, and are in a good agreement with the results predicted by simulation.

Dramatically enhanced impact toughness of two-scale laminate-network structured composites

TMCs are well known materials for their potential use in many fields. However, there are few research on the toughness especially impact toughness of TMCs. To improve impact property of TMCs, one novel kind of titanium matrix composites with two-scale laminate-network structure was fabricated via powder metallurgy and reaction hot pressing. From macro-scale, the novel composites were constituted by Ti6Al4V alloy layers and TiBw/Ti6Al4V composite layers. Moreover, the composite layer exhibited network structure and refined matrix microstructure from micro-scale. Layer thicknesses were well controlled by the masses of Ti6Al4V powder and TiB2-Ti6Al4V mixture powders, and the volume fraction of TiBw reinforcement in the composite layer was adjusted by controlling TiB2 raw material. Bending test results exhibited that the ultimate strain of two-scale composite doubled while bending strength was similar compared with TiBw/Ti6Al4V composites. The impact toughness of two-scale composites was nearly fivefold enhanced compared with monolithic TiBw/Ti6Al4V composites. This phenomenon can be attributed to the introduction of laminate structure, microstructure refinement and interface crack deflection. The analysis of impact curves and fractographs suggests that introducing Ti alloy layers can enhance plastic stage. Increasing TiBw reinforcement volume fractions can enhance the energy absorbed during crack propagation stage.

CHARACTERISATION AND MONITORING OF TI6AL4V (ELI) POWDER USED IN DIFFERENT SELECTIVE LASER MELTING SYSTEMS

The characterisation and monitoring of Ti6Al4V (ELI) feedstock powder is an essential requirement for the full qualification of medical implants and aerospace components produced in selective laser melting systems. Virgin and reused samples of this powder were characterised by determining their physical and chemical properties through techniques complying with international standards. This paper presents the results obtained for Ti6Al4V (ELI) powder of two different particle size distributions received from the same supplier. The characteristics of these powders after several reuse cycles in two different selective laser melting systems are also presented and discussed.

Functionalization of Biomedical Ti6Al4V via In Situ Alloying by Cu during Laser Powder Bed Fusion Manufacturing.

The modern medical industry successfully utilizes Laser Powder Bed Fusion (LPBF) to manufacture complex custom implants. Ti6Al4V is one of the most commonly used biocompatible alloys. In surgery practice, infection at the bone–implant interface is one of the key reasons for implant failure. Therefore, advanced implants with biocompatibility and antibacterial properties are required. Modification of Ti alloy with Cu, which in small concentrations is a proven non-toxic antibacterial agent, is an attractive way to manufacture implants with embedded antibacterial functionality. The possibility of achieving alloying in situ, during manufacturing, is a unique option of the LPBF technology. It provides unique opportunities to manufacture customized implant shapes and design new alloys. Nevertheless, optimal process parameters need to be established for the in situ alloyed materials to form dense parts with required mechanical properties. This research is dedicated to an investigation of Ti6Al4V (ELI)-1 at % Cu material, manufactured by LPBF from a mixture of Ti6Al4V (ELI) and pure Cu powders. The effect of process parameters on surface roughness, chemical composition and distribution of Cu was investigated. Chemical homogeneity was discussed in relation to differences in the viscosity and density of molten Cu and Ti6Al4V. Microstructure, mechanical properties, and fracture behavior of as-built 3D samples were analyzed and discussed. Pilot antibacterial functionalization testing of Ti6Al4V (ELI) in situ alloyed with 1 at % Cu showed promising results and notable reduction in the growth of pure cultures of Escherichia coli and Staphylococcus aureus.