Study On Preparation And Constrained Recovery Properties Of Columnar Grain CuAlBe Shape Memory Alloy

Shape memory alloys are widely used in biomedicine,structural damping and mechanical connectors due to their shape memory effect.Fasteners are one of the applications of shape memory alloys.The use of columnar crystal texture can strengthen the shape memory effect of Cu-based shape memory alloys,and obtain better application performance and lower material cost.It is proposed to use columnar crystal CuAlBe alloy as the fastener for interference connection.The subject comes from the research work of the"Shape Memory Alloy Fastener Connection Technology"project(project number:61409230506)carried out in recent years.The columnar crystal CuAlBe shape memory alloy as a fastener is systemati cally studied mainly from four aspects:preparation process and basic performance characterization,compression performance below Mf temperature,constrained recovery phase transition,and connector performance characterization.Specific work content includes:(1)Designed a set of vertical downward Ohno continuous casting directional solidification equipment for the preparation of columnar crystal CuAlBe shape memory alloy bars with diameters of 8 mm and 12 mm.Observed by metallographic microscope,its structure is a columnar crystal grown along the axial direction of the rod,and its composition is Cu-11.8Al-0.52Be(wt%).The four phase transition characteristic temperatures Ms,Mf,As and Af were measured by DSC to be-76.26?,-81.29?,-65.05?and-54.73?.Before application,the solution treatment of water quenching after 850?heating hold for 30min is used to eliminate the hard and brittle?₂ phase in the alloy and obtain better overall performance.(2)Under the temperature of-100?,unidirectional compression experiments were conducted on compressed samples with polycrystalline,along the growth direction of columnar crystals and perpendicular to the growth direction of columnar crystals,and the corresponding critical compressive stress and strain are(823Mpa,11%)and(1209Mpa,13.8%).,(865MPa,16.7%).The columnar crystal sample has a stress plateau caused by martensite reorientation due to the uniformity of the orientation between the grains,and the nearly parallel interlaced characteristics of the columnar grains are similar to the layered stacking structure of biological shells.The samples perpendicular to the growth direction of columnar crystals have better toughness and plasticity due to the two plasticization mechanisms of martensite reorientation and progressive crack growth,and the overall performance is better.(3)At a temperature of-196?,the sample perpendicular to the growth direction of the columnar crystal is compressed with different compression ratios from 2%to 16%,then make it recover freely.It is found that the rebound amount and the compression amount have a linear relationship with a positive correlation,and the residual strain S and the compression strain?have a linear relationship with a positive correlation at 0<??10%and 12???16%,respectively.And at a certain point within the range of 10%-12%compressive strain due to sudden changes.The maximum compressive strain is10%.(4)At a low temperature of-196°C,the CuAlBe alloy rod was subjected to 10%radial compression and inserted into the sample hole to form a constrained connection sample with an interference amount of 5%.And conduct phase detection and connection effect evaluation.It is concluded that the constrained connection sample has a good interference connection effect.There is residual martensite after constrained recovery.The type of martensite is?'martensite with a 2H structure.There is stabilization of martensite in the constrained recovery process,which ensures the stability of the joint effect of the constrained joint specimen within a certain temperature range.