Influence of hydrogen content on room temperature compressive properties of Ti-6Al-4V alloy at high strain rate

Electromagnetic forming tests were done at room temperature to reveal the influence of hydrogen content on the compressive properties of Ti-6Al-4V alloy at high strain rate. Microstructure was observed to reveal the mechanism of hydrogen-enhanced compressive properties. The experimental results indicate that hydrogen has favorable effects on the compressive properties of Ti-6Al-4V alloy at high strain rate. Compression of Ti-6Al-4V alloy first increases up to a maximum and then decreases with the increase of hydrogen content at the same discharge energy under EMF tests. The compression increases by 47.0% when 0.2% (mass fraction) hydrogen is introduced into Ti-6Al-4V alloy. The optimal hydrogen content for cold formation of Ti–6Al–4V alloy under EMF was determined. The reasons for the hydrogen-induced compressive properties were discussed.

High pressure EIGA preparation and 3D printing capability of Ti-6Al-4V powder

Ti-6 Al-4 V alloy powder was processed by electrode induction melting gas atomization(EIGA)at high gas pressure(5.5-7.0 MPa).The effects of atomizing gas pressure on the powder characteristics and the microstructure,along with the mechanical properties of the as-fabricated block by laser melting deposition(LMD),were investigated.The results indicate that the diameters of powders are distributed in a wide range of sizes from 1 to 400μm,and the median powder size(d50)decreases with increasing gas pressure.The powders with a size fraction of 100-150μm obtained at gas pressures of 6.0 and 6.5 MPa have better flowability.The oxygen content is consistent with the change trend of gas pressure within a low range of 0.06%-0.20%.Specimens fabricated by LMD are mainly composed ofα+βgrains with a fine lamellar Widmanstatten structures and have the ultimate tensile strength(UTS)and yield strength of approximately 1100 and 1000 MPa,respectively.Furthermore,the atomized powders have a favorable 3 D printing capability,and the mechanical properties of Ti-6 Al-4 V alloys manufactured by LMD typically exceed those of their cast or wrought counterparts.

Effect of hydrogen content and stress state on room-temperature mechanical properties of Ti-6Al-4V alloy

This work aims to investigate the effects of hydrogen content(in the range of 0%-0.5%,mass fraction)and stress state (tension and compression)on the room-temperature mechanical properties of Ti-6Al-4V alloy through mechanical properties tests. The effects of hydrogen content on microstructure evolution of Ti-6Al-4V alloy is also examined by optical microscopy,X-ray diffractometry,transmission electron microscopy and scanning electron microscopy.The results show that hydrogen content and stress state have important effects on the room-temperature mechanical properties of Ti-6Al-4V alloy.Tensile strength and ultimate elongation decrease with increasing the hydrogen content,while compressive strength and ultimate reduction are improved after hydrogenation.The reason is that the intergranular deformation dominates at the state of tension.Hydrogen atoms in solid solution and hydrides at grain boundaries increase with increasing the hydrogen content and they can promote the initiation and propagation of cracks along grain boundaries.While the intragranular deformation dominates at the state of compression.The plastic beta phase and hydrides increase with increasing the hydrogen content and they improve the ultimate reduction and compressive strength.

Preparation and Interfacial Stability of SiC_f/Ti-6Al-4V Composites Fabricated Using Powder Coated Fiber Method

SiCf/Ti-6Al-4V composites were fabricated by the powder-coated fiber method. The precursor fiber was prepared under the optimized parameter, and the composites were made using the vacuum hot pressure method. The influence of heat exposure time on products of thelinterfacial reaction was investigated using scanning electron microscope （SEM） and analytical transmission electron microscope （TEM） with energy dispersive spectrometer （EDS）. The main products are TiC and Ti5Si3 after vacuum exposing the samples at 700℃ for 50 h. The growth dynamics of interracial reaction products was analyzed quantitatively, which fitted the parabola rule. The activity energy of the reaction was 252 kJ·mol^-1.

Effect of Powder Particle Size on the Fabrication of Ti-6Al-4V Using Direct Laser Metal Deposition from Elemental Powder Mixture

Direct LMD （laser metal deposition） was used to fabricate thin-wall Ti-6Al-4V using the powder mixture of Ti-6 wt.%Al-4 wt.%V. SEM （scanning electron microscopy）, OM （optical microscopy） and EDS （energy dispersive spectroscopy） were employed to examine the chemical composition and microstructure of the as-deposited sections. Vickers hardness tests were then applied to characterize the mechanical properties of the deposit samples which were fabricated using pre-mixed elemental powders. The EDS line scans indicated that the chemical composition of the samples was homogenous across the deposit. After significant analysis, some differences were observed among two sets of deposit samples which varied in the particle size of the mixing Ti-6wt.%Al-4wt.%V powder. It could be found that the set with similar particle number for Ti, Al and V powder made composition much more stable and could easily get industry qualified Ti-6Al-4V components.

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.

Refinement of α′Martensite by Oxygen in Selective Laser Melted Ti-6Al-4V

Oxygen is crucial in influencing the microstructure evolution of selective laser melted(SLMed)Ti–6Al–4V,significantly impacting its applicability in various sectors.Therefore,this study investigates the influnce of oxygen on microstructure evolution,particularlyα′martensite transformation and refinement mechanisms.Four alloys,Ti–6Al–4V–xO(x=0.11,0.16,0.21,and 0.25 wt%),were fabricated by the SLM process.The martensite start temperature(M_(s))of Ti–6Al–4V,as evaluated by computation,is 656.8°C,and oxygen was found to increase the M_(s) by about 10°C per 0.1 wt%.The SLMed alloy samples exhibit[001]_(β)growth texture along the build direction.Crystallographic analysis of martensite morphology suggests internal twinning on{1011}planes as the lattice invariant strain,which becomes more predominant with increasing oxygen content.Refinement of α′martensite plates by oxygen is due to increased lattice distortion,reduced prior β grain size,and oxygen segregation toβgrain boundaries.Our findings contribute to improving the understanding of the effect of oxygen on the transformation mechanism ofα′martensite during SLM of Ti–6Al–4V.

Microstructural Changes of T1-6A1-4V Matrix by the Incorporation of Continuous SiC Fibers

In SiC（f）/Ti-6Al-4V composites, the microstructure of the matrix close to the fiber was different from that of the fiber-less material. Microstructure observations show that a layer of fine grains was located adjacent to the fiber, and more dislocations and faults were found in this region. Higher recrystallization nucleation rate due to the undeformed SiC fiber and thermal residual stress induced during cooling from the fabrication temperature caused the microstructural changes of the matrix. Hardness measurement indicates that the matrix in the fiber neighborhood was strengthened, and the strengthening effect decreased with distance away from the fiber.

Targeted heat treatment of additively manufactured Ti-6Al-4V for controlled formation of Bi-lamellar microstructures

Laser powder bed fusion(L-PBF)was utilized to produce specimens in Ti-6Al-4V,which were subjected to a bi-lamellar heat treatment,which produces microstructures consisting of primary α-lamellae and a fine secondary α-phase inside the inter-lamellar β-regions.The bi-lamellar microstructure was obtained as(i)a direct bi-lamellar heat treatment from the asbuilt condition or(ii)a bi-lamellar heat treatment preceded by a β-homogenization.For the bi-lamellar treatment with β-homogenization,cooling rates in the range 1-500 K/min were applied after homogenization in β-region followed by inter-critical annealing in the α+β region at various temperatures in the range 850-950℃.The microstructures were characterized using various microscopical techniques.Mechanical testing with Vickers hardness indentation and tensile testing was performed.The bi-lamellar microstructure was harder when compared to a soft fully lamellar microstructure,because of the presence of fine α-platelets inside the β-lamellae.Final low temperature ageing provided an additional hardness increase by precipitation hardening of the primary α-regions.The age hardened bi-lamellar microstructure shows a similar hardness as the very fine,as-built martensitic microstructure.The bi-lamellar microstructure has more favorable mechanical properties than the as-built condition,which has high strength,but poor ductility.After the bi-lamellar heat treatment,the elongation was improved by more than 250%.Due to the very high strength of the as-built condition,loss of tensile strength is unavoidable,resulting in a reduction of tensile strength of~18%.

Hydrogenation behaviors and characteristics of bulk Ti-6Al-4V alloy at different isothermal temperatures

The bulk Ti-6Al-4V alloy was hydrogenated at the temperature range of 723-973 K,and the hydrogen absorption characteristics and hydrogen absorption kinetics were investigated.The results show that there are two types of hydrogen absorption characteristics at different temperatures.The hydrogen content decreases,and the time reaching reaction equilibrium is shorten with the isothermal hydrogenation temperature increasing.Meanwhile,the mechanism of the hydrogen absorption kinetics is different at different temperatures.The incubation period exists at the initial hydrogen absorption stage below 823 K,and K(a2)(the reaction rate constant of Stage 2)>>K(a1)(the reaction rate constant of Stage 1).And there is no incubation period over 823 K,K(a1)>>K(a2).

Characterization of Prealloyed Ti–6Al–4V Powders from EIGA and PREP Process and Mechanical Properties of HIPed Powder Compacts

Prealloyed Ti-6Al-4V powders were prepared by electrode induction melting gas atomization （EIGA） and plasma rotating electrode process （PREP） in this work. A comparative study of EIGA and PREP powders for hot isostatic pressing （HIPing） compaction was conducted. Characterization of important technological parameters such as particle size distribution, powder surface morphology and flowability was carried out. Microstructure and mechanical properties of Ti- 6Al-4V powder compacts HIPed from EIGA and PREP powders were also investigated. The results showed that the EIGA powder has a finer average particle size and higher tap density, while the PREP powder has better flowability and less pores. Micropores can be observed in heat-treated EIGA powder compacts by X-ray tomography and the porosity was found to be about 0.02%. There are no micropores （≥4 μm） to be detected in heat-treated PREP powder compacts. Transgranular fracture mode as well as micropores contributes to the scatter in fatigue property of heat-treated PREP powder compacts. The respective advantages and disadvantages of both EIGA and PREP powders for producing Ti-based complex parts through HIPing were also discussed.