The Temperature Field Simulation Of Fine Grain TC4 Titanium Alloy And Studying Of Grain Growth

Fine grain TC4 titanium alloy has pretty well mechanical property and anticorrosion which is widely used in Aerospace. But the heat affected zone (HAZ) in process of welding roughens serious and performance decreases. So the study of the microstructure and the law of the grain growth is very important for controlling of roughening in (HAZ) and improving performance.The appearance feature of welded-joint of fine TC4 titanium alloy grain and the rule of change for the property of joint is researched in this paper . The method of finite element is used for the simulation of temperature field of thin plate of fine grain TC4 titanium alloy in TIG. the characteristic of the thermal cycling in different zone of the (HAZ) is analyzed. Thermal simulation method is employed to research influences for the final state in tissue transformation and the law of the grain growth in different cooling rates .When the fine grain TC4 titanium alloy was heated by TIG arc, there was a gradually change in grain size and structure from base-material, grain-refining zone, coarse grain zone to fusion zone. There was a grain coarsening behavior in each HAZ area and the grain size changed from severalμm to hundreds ofμm. Fusion zone consisted of coarse columnar crystals. And all the micro-structures were coarseα′needle. Coarse grain area has the structure of equiaxed grains and there areα′needles ,residualβandαphase in its micro-structure. But the size ofα′needles is relatively smaller to seam zone. Grain-refining zone consists of fine equiaxed grains and the micro-structure is also the mixture ofα′needles , residualβandαphase. But in this case, theα′needles are smaller and residualβare bigger. The analyses of temperature field revealed that the longer distance from HAZ to welded joints, the bigger the cooling rate. At the same time, the cooling rate turned slower with the increase of heat input at the same place.The results of thermal simulation showed that the trend of growing becomes smaller with the increase of cooling rate and the main products of this change which in low temperature areα′+αphase and residualβ. Contrarily, the trend of growing becomes bigger and the main products which in high temperature areα′phase . Cooling rate and the time in high temperature also affected a lot to the hardness of HAZ. With the increase of cooling rate, the hardness of HAZ increased, but decreased with the increase of time in high temperature.