Preparation And Properties Of Al-Ti-Zr Intermetallic Compounds

Al-Zr binary alloys and Al-Ti-Zr ternary alloys were synthesized by in-situ reaction of ZrH₂,TiH₂ and Al powder through hot pressing process of 1400-1450?×40.8 MPa×0.5-1h.The phase,the microstructure,the Vickers'hardness,the fracture toughness and the flexural strength of Al-Zr and Al-Ti-Zr alloys with different compositions were studied,and the stabilizing heat treatment properity and oxidation performance of Al-Ti-Zr ternary alloys were also studied.In the Al-Zr binary system,the in-situ synthesis of the samples were successfully finished.The AZ1-0 sample with Al-25at.%Zr contained only the Al₃Zr phase and the AZ0-with Al-33.3at.%Zr contained only Al₂Zr phase.The AZ9-1 sample with Al-25.8at.%Zr and AZ8-2 sample with Al-26.6at.%Zr contained both Al₃Zr and Al₂Zr phase.Some Al₂Zr fine particles were distributed in the grain boundary of the Al₃Zr phase in AZ9-1 sample,which suppressing the growth of Al₃Zr grains effectively.Vickers hardness had a weighted relation with the volume ratio of Al₂Zr phase;while the fracture toughness decreased with the increase of the volume ratio of Al₂Zr phase.The flexural strength of Al-Zr binary alloys were about 100 MPa,and the fracture mode was transgranular fracture.Al40 sample with Al-40at.%Ti-20at.%Zr,Al41 sample with Al-45at.%Ti-14at.%Zr and Al43 sample with Al-47at.%Ti-10at.%Zr contained Ti₃Al+TiAl+Al₃?Zr,Ti?₅ phases and the ratio of Ti₃Al+TiAl phase rose from Al40,Al41 to Al43 sample.Al47 sample with Al-38at.%Ti-15at.%Zr and Al50 sample with Al-30at.%Ti-20at.%contained TiAl+?Al,Ti?₂Zr+Al₃?Zr,Ti?₅ phases and Al54 sample with Al-35at.%Ti-11at.%Zr contained TiAl+?Al,Ti?₂Zr phases.In addition to the Ti₃Al+TiAl lamellar structure,Ti₂Al+TiAl and Ti?Zr?Al+Al₃?Zr,Ti?₅ lamellar structures were found in Al-Ti-Zr ternary alloys,and Al-Zr intermetallics were found in the form of massive structures.Mechanical performance studies showed that the vickers hardness of Al-Ti-Zr ternary alloys increased with the increase of Al-Zr intermetallic compounds,while the fracture toughness and flexural strength increased with the proportion of Ti₃Al+TiAl lamellar structure.The deflection of the cracks in the lamellar played a key role in improving the fracture toughness and the interlaminar fracture also played a key role in improving the flexural strength.The fracture mode of the alloys were transgranular fracture.When the cracks met the lamellar structure,the cracks deflection would occurs and the crack growth steps were formed,resulting the increase of the energy consumption of crack propagation.Thus,the fracture toughness and the flexural strength of the alloys were improved.Among the Al-Ti-Zr alloys,Al41 alloy had better comprehensive performance,which had the vickers hardness,fracture toughness and flexural strength of 568±38 HV,5.2±0.6MPa.m^1/2 and 369±9 MPa,respectively.Thermal stabilization treatment at 700⁸00°C is not only beneficial to improve the stability of the structure of the alloys and the mechanical properties,but also refined the microstructures.After the 800°C×32h stabilization heat treatment,the vickers hardness,fracture toughness and flexural strength of Al41 alloy reached up to 606±36 HV,6.6±0.4 MPa.m^1/2 and 510±20 MPa,respectively.Increased by6.7%,26.9%,and 38.2%compared with the original sample.Al41 sample had good oxidation resistance at 700⁸00°C,but it had poor oxidation resistance at 900°C and 1000°C.The difference in thermal expansion coefficient between different oxides would cause the spalling of oxides in the cooling process.So the Al41 alloy was suitable for use at 800°C.The oxidation model of Al41 alloy was proposed:in the initial stage of oxidation,the Ti₃Al and TiAl phases exposed on the surface of the alloy would react with O in the air to form TiO₂ and Al₂O₃ oxide films firstly.Due to the rapid growth rate of TiO₂ and loose property of TiO₂ oxide film,the TiO₂ oxide film would continuously thickened and it would locate in the outermost layer of the oxide film.On the surface of Al₃?Zr,Ti?₅ phase,a dense oxide film composed of Al₂O₃,ZrO₂ and a small amount of TiO₂were formed,which would inhibit the outward diffusion of atoms in the alloy and the inward diffusion of O,resulting the growth of the oxide film became slow.After oxidation at high temperature for a long time,the TiO₂ oxide film formed by the adjacent Ti₃Al and TiAl phases expanded outward and eventually spread over the entire surface.Therefore,high Al and Zr content in the Al-Ti-Zr alloys were beneficial to improve the oxidation resistance of the alloy.