Study On The Microstructure Evolution Of Simi-solid Ti-7Cu Alloy After Heat Treatment

Titanium alloy is widely used in the military and civilian field,because of its high performance such as high temperature resistant,resistant to corrosion,high specific strength,good biological compatibility and non-magnetic.However,the high processing cost of titanium alloy had been serious problems to researchers related.Compared with traditional casting technology,Semi-solid forming technology is expected to realize the low cost for titanium alloy because of its low forming force.At present,semi-solid forming technology of magnesium and aluminum alloy has been well studied,but semi-solid forming technology of titanium alloy is still less researched.This article is aim to study the influence of heat treatment conditions,such as processing temperature and isothermal time as well as cooling method,on the microstructure of Ti-7Cu alloy.The characteristics such as average grain size,shape factor and grain growth activation energy were calculated,grain grew up mechanism and the effects of different cooling methods on alloy microstructure were also analyzed.The main experimental results showed that grain size and shape factor increased with the rising of temperature.It is found that the grain size increased with increasing temperature.When the temperature rises to a certain extent,the grain size became normally.Grain growth activation energy was also affected by temperature,with the increase of temperature,the grain growth activation energy decreased gradually at different temperature stages.When the temperature was under 1200?,the grain grew up mainly by combining growing up mechanism,and when the temperature was higher than 1200?,growing up transformed into to Ostwald ripening mechanism primarily.With the extension of isothermal time,the average grain size presented exponential growth trend.Changing trend of grain shape factor with time is different under different temperature.Grain growth exponent of Ti-7cu alloy at semi-solid temperature was 0.71 under 1100? and 0.86 under 1200? respectively.The influence of cooling methods on alloy microstructure was significant.The grain size after furnace cooling is larger than that after oil cooling,and precipitated phase were flake and granular layer.However after air cooling there had no obvious boundary,and scattered with launching.The change of cooling method does not change the alloy organization room temperature.Hardness was determined after different heat treatment of the alloy under the conditions of found that hardness value reduced with the increase of temperature.Effect of isothermal time on Ti-7cu alloy hardness value has no disciplinary change.Cooling method had a greater influence on the hardness of alloy.The hardness after oil cooling was the highest.