片状组织TC21钛合金的显微组织−断裂韧性关系及韧化机制

摘要

研究显微组织参数对片状组织TC21钛合金断裂韧性的影响.通过三重热处理获得片状组织,并采用OM和SEM方法对显微组织进行表征.单相区的冷却速率和两相区的固溶温度决定α片的尺寸及含量,而时效温度则主要控制次生α片的析出行为.α片含量、厚度以及次生α片厚度是影响TC21钛合金断裂韧性的重要组织参数.提高α片含量、增加α片(或次生α片)厚度均能提高TC21钛合金的断裂韧性.基于α片裂纹尖端塑性区能量消耗,提出钛合金韧化机制.%The independent influence of microstructural features on fracture toughness of TC21 alloy with lamellar microstructure was investigated. Triple heat treatments were designed to obtain lamellar microstructures with different parameters, which were characterized by OM and SEM. The size and content ofα plates were mainly determined by cooling rate from singleβ phase field and solution temperature in two-phase field; while the precipitation behavior of secondaryα platelets was dominantly controlled by aging temperature in two-phase field. The content and thickness ofα plates and the thickness of secondaryα platelets were important microstructural features influencing the fracture toughness. Both increasing the content ofα plates and thickeningα plates (or secondaryα platelets) could enhance the fracture toughness of TC21 alloy. Based on energy consumption by the plastic zone of crack tip inα plates, a toughening mechanism for titanium alloys was proposed.