Effect Of Deformation And Heat Treatment On The Microstructure And Mechanical Properties Of Zrtialv Alloy

ZrTiAlV alloy possesses an excellent comprehensive property, such as high strength,low density, perfect low temperature resistance, excellent radiation resistance andoutstanding atomic oxygen corrosion resistance which makes it can be used as thesubstitution of steel and titanium alloy to fabricate the key moving components of spaceservice aircrafts. In this dissertation, the object of the research was Zr40Ti5Al4V alloy.The effect of cold rolling deformation, suface deformation produced by high speedpounding (HSP) and the followed heat treatment on the microstructure evolution andmechanical properties of the alloy were studied, with an aim of controlling themicrostructure and mechanical properties.The alloy after solution treatment was cold rolled at room temperature. Thebody-centred cubic β phase partially transformed to orthorhombic α″phase due tostrain-induced phase transformation during the deformation process, with a definiterelationship [001]α″∥[110]βbetween the two phases. The continuous surface deformationresulted in a transformation process of β→β+α″→β+α(α′). The accumulated dislocationsduring the deformation process and the high strength phase α/α′increased the strength ofthe alloy. Moreover, the peak hardness existed in the subsurface due to the maximumequivalent strain appeared in the subsurface during the surface deformation process.The decreased dislocation density during the heat treatment process made thestrength of the alloy lower. And the mechanical properties of the alloy depended on theultimate phase composition. For the common heat treatment, the majority α phase formedduring the furnace cooling process (FC) led to a high strength and low ductility. More βphase was retained after air cooling (AC) treatment. And a full β phase microstructure wasproduced when the isothermal temperature increased to700oC, with an ultimate tensilestrength of951MPa and an elongation of17.0%. A relationship between β grain size Dand temperature T, i.e. D=5.7×105exp(-1.78×104/T), was established under a condition ofT=700-850oC according to statistical results. When the electropulsing treatment wascarried out on the deformed alloy, the phase transformation and recrystallization were promoted simultaneously and the grains were refined remarkablely. The graduallyincreased peak current density resulted in a transformation process of β+α″→β+α→β.When the peak current density increased to1.92kA·mm-2, the grain size was reduced to~26μm with the initial grain size of~346μm.