Papers by Keyword: Ti₆Al₄V Alloy

Abstract: An inorganic metal modified silicate composite coating was developed to protect the corrosion and oxidation of Ti6Al4V alloy at 650°C. The properties of the coatings were investigated by oxidation and corrosion experiments, and the microstructure of the coatings was studied by SEM. The isothermal oxidation results indicated that the Ti6Al4V alloy suffered serious oxidation after exposed for 100h at 650°C and the mass of the alloy gained almost lineally, while the coated alloy had almost no mass gain and the coatings keep intact after oxidation. The salt spray test for 20h and oxidation at 650°C for 2h was carried out to investigate the corrosion and oxidation properties of the coatings. The results indicated that the alloy experienced serious corrosion after experiment for 20 cycles, while the coated alloy did not corrode after the experiments. The thermal shock experiments indicated that the coatings could withstand 50 times thermal shock when kept for 5min at 700°C and then immediately put into 3.5%NaCl solution at room temperature.

Abstract: Titanium alloys are often material of choice for aerospace, chemical and biomedical industries, because of their unusual corrosion resistance, high mechanical strength and low density. However titanium alloys have very poor wear resistance. Hard coatings can be formed on the surface of titanium alloys to improve their tribological property. In this work ion nitriding without hydrogen technique was used to treat Ti-6Al-4V alloy and the nitrided layer was formed on the substrate surface. The fundamental coating properties, such as the phase, component, hardness and elastic modulus were investigated. At the ion-nitriding condition of flux ratio N2/Ar=1:1, pressure 40 pa and substrate temperature 900°C, the nitrided layer was formed. The layer consists of Ti2N and TiN compound. The content of element nitrogen in the nitrided layer gradiently decreases from the the surface to the substrate direction. For a better understanding of the hardness of the nitrided layer, the nano indentation test and microhardness test are both used. The results show that the average values of hardness and elastic modulus for the surface of the nitrided layer are 17.36GPa and 328.81GPa, about 6 times and 3 times respectively as those of Ti-6Al-4V substrate. The hardness of the nitrided layer decreases from the surface to the substrate direction, which corresponding to the content change of element nitrogen. For the result of nano indentation test, when the indentation depth is more than 400nm, the values of hardness and elastic modulus both decrease with the increase of the indentation depth. It is because of the influence of the soft Ti-6Al-4V substrate.

Abstract: The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian laser heat source to predict the depth of the heat-affected zone (HAZ) and temperature distribution in a Ti6Al4V alloy workpiece. It is found that the temperature profile and depth of HAZ are strongly dependent on the parameters of the laser beam. The thermal model simulations are compared with results produced by experimental work and these show close agreement.

Abstract: Removal of heat from the cutting zone is critical when machining titanium. The application of high pressure coolant during turning of titanium results in longer tool life and better surface finish. In this paper, the effect of the application of cutting fluid at high pressure during the milling of titanium alloys is presented.

Abstract: By means of the measurement of creep curves and microstructure observation, the influence of T6 heat treatment on the microstructure and creep properties of the wrought Ti-6Al-4V the alloy has been investigated. The experimental results showed that the microstructure of the wrought alloy consists of the strip-like +  phases, which results in the alloy displaying a higher strain rate and shorter creep life under the test condition of 575 MPa and 400°C. After T6 treatment, the creep life of the alloy at same conditions enhanced to 548 h from 66 h. Microstructure of T6 treated alloy consisted of the primary  and /phases, and signification amount of the bundle-likephase precipitated along the different orientations in the grains, this is a main reason of enhancing creep life of the alloy. During forging, the denser dislocation rows were activated in the local region of the matrix in the alloy. During creep, the deformed mechanism of the alloy was the double orientations slip of and dislocations activated on the pyramidal planes in  phase.

Abstract: A zircon coating was applied on the surface of Ti-6Al-4V alloy by plasma spray and its effect on the high temperature tensile properties of the alloy as well as the oxidation behavior of the alloy were studied. Tensile tests were conducted at 850°C with different strain rates of 10-4s-1,10-3s- 1, 10-2s-1 and 10-1s-1. The results show that the elongation of the coated specimens is higher than that of the uncoated ones, while the ultimate tensile strength of the alloy is not changed. An oxide film had formed on the surface of uncoated Ti-6Al-4V alloy, however no such oxide film was found on the coated alloy at the early of stage. The coating can prevent oxygen penetration into the substrate thus prevent embrittlement of the subsurface zone. The ductility could be improved by means of the zircon coating. The optical micrographs of the specimens show little change in microstructures of the coated and uncoated specimens. Zircon coating has no effect on the microstructure of the substrate alloy.

Abstract: Ti-6Al-4V was successfully jointed by linear friction welding (LFW). A sound weld of thickness of 65-115 $m was obtained under the present conditions. The weld consisted of the superfine α+β structure, which is associated with the rapid heating and cooling processes involved in LFW. The thermomechanically affected zone (TMAZ) was limited and comprised of the severely deformed α and β grains. In the flash, a gradual microstructure was formed from the weld edge to the flash edge. A martensite structure (α’) was formed besides the acicular α+β in the flash edge owing to the fast cooling rate.

Abstract: Investigations have been conducted on the fatigue behavior of Ti-6Al-4V alloy with the bimodal microstructure in air at room temperature, in vacuum at room temperature and in vacuum at low temperature (100K), respectively. The results show that the fatigue life of this alloy is longer in vacuum and/or at low temperature than that in air at room temperature. The combination of vacuum and low temperature can much improve the fatigue properties of this alloy because of their purifying effect on fatigue cracks propagation. SEM observation of fatigue fracture surface indicates that all the fatigue cracks initiate in the sample surface when Nf ≦106 cycles. The above three testing conditions lead to different modes of fatigue crack propagation and therefore much different morphology of fatigue fracture.

Abstract: Now the oxidation-resistant glass-ceramic coatings have been widely used in reducing surface oxidation of Ti alloys during heat process. In present investigation, a lead-free glass-ceramic coating with wider protection temperature range was developed to protect Ti-6Al-4V alloy from oxidation. The phase compositions of the present coating and the oxygen distributions in the surface layers of Ti-6Al-4V specimens were investigated by means of XRD, as well as the metallographs of cross-section were observed and the depths of oxidized layers were determined by microhardness analysis. The results show that the present glass-ceramic coating can provide the oxidation-resistant effect over the temperature range of 500-1000oC in ambient air, with an environmentally friendly lead-free coating composition.

Abstract: Titanium alloys are widely used in the aerospace industry for applications requiring high strength at elevated temperature and high mechanical resistance. However, titanium alloys are classified as extremely difficult-to-cut materials owing to their physical, chemical, and mechanical properties, which result in the low material removal rate and the short tool life. This paper presents an experimental research of the tool wear patterns and relevant wear mechanisms during high-speed milling of Ti-6Al-4V with cemented carbide inserts. SEM-EDX analysis showed that nose wear and edge wear were the main tool failure modes during high-speed milling process, which were different from the wear patterns under traditional cutting conditions. Adhesion, attrition and diffusion wear mechanisms, as well as the cracks were responsible for the tool wear.