激光选区熔化TC11钛合金的断裂机理及异种载荷下裂纹扩展研究

Fracture Mechanism and Crack Propagation of TC11 Titanium Alloy Melted by Laser Selective Melting under Different Loads

目的基于航天航空领域损伤容限性钛合金的设计理念,研究沉积态TC11钛合金拉伸速率相关的断裂机理及异种载荷形式下裂纹扩展路径。方法采用电子背散射衍射(EBSD)表征由激光选区熔化(SLM)制备的沉积态TC11钛合金的晶粒形貌,利用扫描电子显微镜分析不同应变速率下TC11钛合金的断口形貌和缺陷分布,针对无法原位实时追踪裂纹扩展路径的问题,利用Abaqus相场UEL对裂纹扩展进行研究。结果沉积态TC11钛合金中,∥BD截面上的晶粒主要为柱状晶并有少部分等轴晶,⊥BD截面上的晶粒全部为等轴晶,组织为由密排立方结构(HCP)的针状α相构成的马氏体,无明显晶粒取向;瞬时载荷下,载荷为1、1.5、2 MPa时,切向裂纹宽度分别为0、7.69、14 mm,角度分别为108°、92°、82°;周期载荷下,载荷为1、1.1、1.2、1.35、1.5 MPa时,裂纹宽度分别为15.56、11.87、26.23、20.51、20.92 mm。结论随拉伸速率的增加,断裂机理由韧性断裂转化为脆性断裂;瞬时加载时,裂纹萌生并切向扩展,进而裂纹分叉直至完全断裂,且载荷的增加对沉积态TC11钛合金切向裂纹有促进作用,同时可抑制裂纹的分叉;周期加载时,载荷的增加对裂纹宽度先是起促进作用,裂纹达到最大值后稳定在25~20 mm。

The work aims to study the fracture law and crack propagation path related to the rate of deposited TC11 titanium alloy according to the current design concept of damage tolerant titanium alloy in aerospace field.In this paper,the grain morphology of deposited TC11 titanium alloy prepared by laser selective melting(SLM)was characterized by electron backscattered diffraction(EBSD).The fracture morphology and defect distribution of TC11 titanium alloy under different strain rates were analyzed with scanning electron microscope(SEM).Aiming at the problem that the crack propagation path cannot be tracked in situ and in real time,the Abaqus phase field UEL was used to study the crack propagation.In the deposited TC11 titanium alloy,the grains on the//BD section were mainly columnar crystals and a small part of equiaxed crystals.All the grains on the⊥BD section were equiaxed crystals and the structure was needle like with dense cubic structure(HCP)αphase martensite tissue.No obvious grain orientation was observed;Under instantaneous load,when the load was 1,1.5,2 MPa,the tangential crack width was 0,7.69,14 mm respectively.The angles were 108°,92°,82°respectively;Under cyclic load,when the load was 1,1.1,1.2,1.35,1.5 MPa,the crack width was 15.56,11.87,26.23,20.51,20.92 mm respectively.With the increase of tensile rate,the fracture mechanism changes from ductile fracture to brittle fracture;Under transient loading,the crack initiates and propagates in a tangential sway,and then the crack bifurcates until complete fractures.The increase of load can promote the tangential crack of deposited TC11 titanium alloy and inhibit the crack bifurcation at the same time;During periodic loading,the increase of load promotes the crack width,and then the crack stabilizes at 25~20 mm after it reaches the maximum value.