冷却介质对商业纯钛β→α相转变组织及织构的影响

Influence of Different Cooling Mediums on β→α Phase Transformation Microstructure and Texture in Commercially Pure Ti

利用OM、ECC、EBSD、TEM等表征技术和显微硬度实验研究了经β固溶处理的商业纯钛板材在β→α相变过程中不同冷却介质对其组织演变、变体选择、织构遗传及力学性能的影响。结果表明:随着冷却速率的降低,相变组织依次呈细针状α′马氏体(水冷和液氮冷)、Widmanstatten组织(空冷)及粗大晶粒(炉冷),且冷却速率越快,则转变组织越细,进而其硬度值越高。在β→α冷却过程中,只有炉冷条件下由于出现了部分不满足Burgers关系的取向,导致其并不严格遵循Burgers取向关系。与原始组织相比,水冷和液氮冷条件下由于出现新的织构成分(<0001>//TD、<1120>//ND),导致其织构分布更分散;炉冷条件下由于发生了强烈变体选择而出现织构遗传现象,导致更强的相变织构。因此可以通过提高冷却速率来抑制变体选择,进而弱化相变织构。

The effect of cooling medium on microstructure evolution,variant selection and texture inheritance along with mechanical properties in a recrystallized commercially pure Ti sheet after β-solution treatment was investigated by combined use of optical microscopy(OM),electron channeling contrast(ECC)imaging,electron backscatter diffraction(EBSD)techniques,transmission electron microscopy(TEM)and micro-hardness test.It is found that with the decrease of cooling rate,fine needle-like α'martensite(in water and liquid nitrogen),Widmanstatten(in air),and coarse-grain microstructures(in furnace)are observed in turn.Additionally,the faster cooling rate results in a finer transformed structure accompanied with an attendant higher hardness value.Analyses for crystallographic orientations reveal that the Burgers orientation relationship(BOR)is strictly obeyed during the β→α cooling except for the β-furnace-cooled specimen with appearance of other misorientations disobeying the BOR.As for texture characteristics,firstly,the texture distribution is largely scattered compared with the initial one and new orientation components of<0001>//TD and//ND appear upon the water and liquid nitrogen quenching.Secondly,the texture inheritance phenomenon occurs in furnace cooling condition because of stronger variant selection,then leading to a stronger transformation texture.Results suggest that raising cooling rates can be more feasible to weaken the transformation texture by suppressing the variant selection.