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1.
The Ti6Al4V/(Ni/Al)/Ti6Al4V joints were obtained through reactive resistance welding which takes advantage of electric current heating to initiate the rapid exothermic reaction of Ni(V)/Al multilayers and activate diffusion of elements across the Ni/Al-Ti6Al4V interfaces. Simulations of temperature distribution, carried out using COMSOL® software, showed temperature gradient in the joint being a result of differences in resistivity of the Ti6Al4V alloy and the (Ni/Al)/Ti6Al4V interface. Shear tests revealed that extending duration of the process from 2 to 6 minutes helped to improve the shear strength from ~?240 to ~?335 MPa. The microstructure observations of the samples after those tests showed that de-cohesion of the joint occurred along the filler material/base material interface. A microcrack network characteristic for reacted Ni/Al foil with small ridges was found on the flat surfaces of fractured samples.  相似文献   

2.
none 《粉末冶金学》2013,56(4):251-257
Abstract

Room temperature tensile ductility is an important property of titanium (Ti) and titanium alloys for structural applications. This article reviews the dependency of tensile ductility on oxygen for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgy (PM) and additive manufacturing (AM) or three-dimensional printing methods and recent advances in understanding the effect of oxygen on ductility. Seven mechanisms have been discussed based on case studies of individual titanium materials reported in literature. The dependency of ductility on oxygen is determined by both the composition and microstructure of the titanium alloy. For Ti–6Al–4V (wt-%), as sintered Ti–6Al–4V shows a critical oxygen level of about 0·33 wt-% while additively manufactured Ti–6Al–4V exhibits different critical levels ranging from about 0·22% to well above 0·4% depending on microstructure. Rare earth (RE) elements are effective scavengers of oxygen in titanium materials even just with a small addition (e.g. 0·1 wt-%), irrespective of the manufacturing method (IM, PM and AM). High cycle fatigue experiments revealed no initiation of fatigue cracks from the resulting RE oxide particles over the size range from submicrometres to a few micrometres. A small addition of RE elements offers a practical and affordable approach to mitigating the detrimental effect of oxygen on ductility.  相似文献   

3.
The effects of Al–5Ti–1B and Al–15Zr master alloys on the structural characteristics and tensile properties of Al–4.5Cu–0.3Mg aluminium alloy were studied. Al–5Ti–1B was found to be more effective than Al–15Zr in grain refining of the alloy. It could be seen that average grain size reduces from 570 to 260?μm when 0.01?wt-% Ti addition; additionally, while different amounts of Ti and Zr were added to the alloy, the dendritic structure changes from long dendrite to rather rosette-like morphology. Furthermore, tensile testing of cast specimens revealed that ultimate tensile strength (UTS) of the cast alloy increases from 241 to 283 and 260?MPa after adding the optimum amount of Ti and Zr containing master alloys, respectively. Moreover, UTS values of T6 heat-treated specimens also showed 73 and 61% improvement after adding 0.05?wt-% Ti and 0.3?wt-% Zr to the alloy. Fracture surface examinations exhibited a transition from brittle fracture mode in as-cast to ductile fracture in refined and T6 heat-treated specimens.  相似文献   

4.
The fatigue properties and the fracture mechanisms of the Ti–6Al–4V alloy produced by selective laser melting (SLM) from a powder of an CL41TiELI titanium alloy have been studied. Cylindrical blanks were grown at angles of 90° and 45° to a platform. The best fatigue strength is observed in the samples the blanks of which were grown at an angle of 45°. It is found that the structure of the SLM material can contain portions with unmelted powder particles, which are the places of initiation of fatigue cracks.  相似文献   

5.
This work deals with the influence of surface mechanical attrition treatment (SMAT) duration on fatigue lives of Ti–6Al–4V. The SMAT process was carried out in vacuum with SAE 52100 steel balls of 5 mm diameter for 30 and 60 min at a vibrating frequency of 50 Hz. SMAT treated surface was characterized by electron microscopy. Surface roughness, nano-indentation hardness, residual stress, and tensile properties of the material in both SMAT treated and untreated conditions were determined. SMAT enabled surface nanocrystallization, increased surface roughness, surface hardness, compressive residual stress and tensile strength but reduced ductility. Samples treated for 30 min exhibited superior fatigue lives owing to positive influence of nanostructured surface layer, compressive residual stress and work hardened layer. However, fatigue lives of the samples treated for 60 min were inferior to those of untreated samples due to presence of microdamages or cracks induced by the impacting balls during the treatment.  相似文献   

6.
《粉末冶金学》2013,56(4):263-266
Abstract

Titanium alloys containing β stabilising elements such as Nb, Zr and Ta are particularly promising as implant materials because of their excellent combination of low modulus, high strength, corrosion resistance and biocompatibility. A low elastic modulus is important for implants to avoid stress shielding and associated bone resorption. The difficulty of producing complex shapes of these alloys by conventional methods makes metal injection moulding (MIM) attractive. Ti–17Nb alloy parts with densities 94% of theoretical have been produced by MIM of a feedstock based on blended elemental powders. Scanning electron microscopy reveals a typical α?β Widmanstätten microstructure with a precipitated α phase layer along the grain boundaries. The parts exhibit an ultimate tensile strength of 768 MPa and a plastic elongation of over 5%. The modulus of elasticity, about 84 GPa, is more than 20% lower than that of cp Ti and Ti–6Al–4V.  相似文献   

7.
The effect of heat treatment on microstructure and mechanical behaviours of direct metal laser sintered Ti–6Al–4V samples have been studied. Rectangular parts were built in two different directions; vertical and horizontal and subjected to two different heat treatment cycles: above β transus and below β transus with air cooling. Surface characteristics, microstructural examination and mechanical properties have been investigated. Below β transus treatment creates a modification in the surface morphology with a fine dimple network. Above β transus treatment leads to extensive grain growth at the middle section of the vertically build component thereby increasing its microhardness. Both the selected heat treatment cycles significantly reduces the tensile strength and improves the elongation when compared to as-sintered material. However, below transus temperature treated vertical built specimen results in optimum combination of tensile strength (1124 MPa) and elongation (20%). Higher coefficient of friction has been recorded for specimens after heat treatment.  相似文献   

8.
The present article describes the influence of microstructure i.e. lamellar, bimodal and equiaxed on solid particle erosion behaviour of Ti–6AL–4V alloy at service exposed temperature i.e. 400 °C. Erosion tests have been carried out using an air jet type test rig and Taguchi’s experimental design. From erosion test, it has been observed that impact velocity is the most significant controlling factor influencing the erosion of Ti–6Al–4V alloy followed by impingement angle, size of erodent and microstructural variation.The results indicated that erosion rate of Ti–6Al–4V alloy was less in bimodal microstructure followed by equiaxed and lamellar microstructure.  相似文献   

9.
Abstract

The effect of minor Zr and Ti elements on microstructures and properties of Al–8·6Zn–2·5Mg–2·2Cu alloys was investigated. The results show that there is no significant change in the grain size by simultaneous addition of Zr and Ti as compared to individual additions of Zr or Ti to Al–8·6Zn–2·5Mg–2·2Cu alloy. The ability of restraining recrystallisation of Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr–0·04Ti alloy is weaker than that of alloy Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy, since Ti and Zr have a poisoning interaction. The corresponding tensile properties, hardness and stress corrosion cracking resistance of the Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy were decreased by addition of Ti.  相似文献   

10.
Titanium (Ti) alloy, Ti–6Al–4V (commonly known as Ti64), is employed in numerous applications due to their superior strength to weight ratio, low cost to performance ratio, tensile strength, and corrosion resistance properties. However, due to its poor tribological (friction and wear) properties and difficult-to-machine material, its implementation in the intended applications is limited. Nevertheless, Ti64 can be accurately machined using wire electrical discharge machining (WEDM) and further, this process develops a recast layer on the surface of Ti64, which posses larger percentage of oxygen. Therefore, in the present work, it is hypothesized that, the presence of the recast layer on the surface of Ti64 may enhance its tribological properties. To validate the proposed hypothesis, pins of (1) pure Ti64 and (2) WEDMed Ti64 were slided against EN32 steel disc on a pin on disc experimental setup for load of 50 N, rotational speed of 200 rpm and sliding distance of 500 m. In-situ analysis (scanning electron microscope and energy dispersive spectroscopy) and mechanical properties (nano-hardness and elastic modulus) were performed on the pin’s surface, to identify the change in properties. Obtained results indicated significant increase in the oxide layer formation, consequently enhanced the tribological properties of WEDMed Ti64 compared to pure Ti64. To understand the tribological behavior of WEDMed Ti64 at other rotational speed and load, second set of experiments was performed by varying load (50, 70 and 90 N) and rotational speed of (200, 400 and 600 rpm). It was observed that wear values were not proportional to increase in load and speed. To identify the condition favoring the tribological behavior, multi-response optimization technique was performed and the identified load and speed values for the optimum tribological behavior were estimated.  相似文献   

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