Study On Microstructure And Properties Of Ti-45Al-2Nb-2Mn Directionally Solidified By Electromagnetic Cold Crucible

TiAl alloy with excellent high temperature performance and excellent oxidation resistance,in the past 20 years,attracted more attention and caused a very wide range of application in the aerospace field.Thus,it promotes the development of high temperature structural materials.However the poor plasticity and fracture toughness at room temperature,is a major obstacle to expand its application.In this study,Ti45Al2Nb2 Mn master alloy ingot was firstly prepared by induction skull melting furnace(ISM)with a water cooled copper crucible in vacuum.And then the Ti45Al2Nb2 Mn alloy ingot with good surface quality and directional macrostructure was prepared by electromagnetic cold crucible directional solidification treatment.A good directional property of Ti-45Al-2Nb-2Mn alloy is achieved by controlling the different draw speed(solidification rate)during the directional solidification process.Shrinkage cavity in original as-cast organization would disappear after directional solidification.In electromagnetic cold crucible directional solidification process,solid-liquid interface shape changes from dendritic-cell dendritic-cellular changes in turn with the increase of solidification rate,while the grain size decrease with the increase of draw speed.Nb,belonging to beta stable elements,can expand beta solidification interval,so in th e process of reaction,? phase is always the primary phase.Since it is 2 d photos,when the ? phase precipitates firstly,the orientation and growth direction of ?2/? fragments layer is not 45° strictly or parallel,but the XRD results and energy spectrum analysis indicate that the organization contains mainly ?2+? duplex layers and a small amount of B2 phase.Compared with the as-cast alloys,the mechanical properties of directional solidificational alloys was improved obviously.After directional solidification treatment the compression strength of Ti Al alloy is up to 1654 mpa,and the compression intensity of the original as-cast alloy is only 899 mpa.Under the same conditions,peak stress of the as-cast alloy is only about 329 mpa,while directional solidification of the alloy is up to 479 mpa.The tensile strength increases as the draw speed addition.The fracture toughness of the columnar crystal layer organization are more than 20MPa·m1/2.Under the condition of the directional solidification,microhardness of alloys increased by 40%-70% compared with that of the original as-cast alloy.Compression fracture mode is mainly tearing fracture and the wear layer fracture is mixed in;ladder-like microsturcture and P type fracture appears in tensile fracture morphology;Fracture toughness morphology are typical brittle cleavage fracture.