Study On Microstructure And Properties And Preparation Of CuAlNi Shape Memory Alloys

In this thesis, groups of CuAlNi shape memory alloys added with Ti,Zr,B and Mnelements were prepared by vacuum nonconsumable arc melting furnace and high frequencyinduction furnace. The effects of alloy elements and heat treatment process onmicrostructure and performance of CuAlNi shape memory alloys were studied byobservation of microstructure, XRD phase analysis, phase transformation temperature andshape recovery rate testing.The ingot quality was greatly affected by smelting process, and the ingot quality ofAtecD high frequency induction furnace was superior to WK-Ⅱ vacuum nonconsumablearc melting furnace.Additions of Ti, Zr, B could refine grain in different degrees, among which B was thebest one. The grains size decreased from1~2mm to150~200μm with B addtion, at the sametime, the coarse column-like grains of alloy were changed into nearequiaxed ones.With increase of Al content, the inclination M18R martensite in as-quenched CuAlNialloys was larger, the phase transformation temperature decreased quickly, and the shaperecovery rate gradually increased. The precipition of γ2phase was suppressed by theincrease of Ni content, at the same time, the transformation temperature decreased，theshape recovery rate increased to a certain extent. The B element in CuAlNi alloy showedsignificantly grain refinement effect and remarkably affected the eutectoid point. The effectgrain refining becomes no more evident with increasing B content when the grains werefined to150~200μm. The CuAlNi alloy added with Mn element showed highertransformation temperature and better recovery rate than ones without Mn.The matensite stripes in CuAlNiMnB alloy broadened and straightened，and thetransformation temperature increased first and then decreased，with the elevation of quenchtemperature. The recovery rate reached the highest value, which was96%, and Ms pointreached171.6℃after quenching treatment at800℃×10min. The ordered degree of alloyand recovery rate both appeared the tendency of first raising then lowering with increasingholding time.The transformation temperature, hardness, stability of shape memory effect wasimproved by tempering treatment. But when alloy were tempered over10min at300℃, themartensite boundaries blurred, γ2begin to precipitate, the shape memory effect of alloy wasseriously weakened. By comprehensive comparative studying groups of alloys, the CuAlNiMnB alloyprepared by high frequency induction furnace has very high engineering value andapplication potentiality, which has uniform composition and fine microstructure, as well ashigh transformation temperature and recovery rate after800℃×10min quenching treatment.