連續(xù)點式鍛壓激光快速成形TC11鈦合金的組織形成過程和力學性能

連續(xù)點式鍛壓激光快速成形TC11鈦合金的組織形成過程和力學性能Microstructures and Mechanical Properties of TC11 Titanium alloy Formed by Laser Rapid Forming and Its Combination with Consecutive Point-Mode Forging

采用連續(xù)點式鍛壓激光快速成形技術進行了TC11鈦合金厚壁零件成形實驗，利用OM、SEM等手段研究了連續(xù)點式鍛壓激光快速成形TC11鈦合金的組織和力學性能。結果表明，TC11鈦合金試樣內(nèi)部的等軸晶晶粒尺寸均勻，平均晶粒尺寸48.7 μm。等軸晶的晶界α相連續(xù)，晶內(nèi)是初生α相板條+β轉變組織組成的雙態(tài)組織。在連續(xù)點式鍛壓激光快速成形過程中，連續(xù)點式鍛壓時，TC11鈦合金厚壁零件的表層變形區(qū)深度約為1.5 mm，變形量為20%。在連續(xù)點式鍛壓冷變形TC11鈦合金上表面沉積新層過程中，當激光束掃描經(jīng)過時，熔池熱影響區(qū)中約1 mm厚(4層)冷變形TC11鈦合金被加熱到鈦合金β轉變溫度之上，并在0.86 s內(nèi)完成再結晶。力學性能結果表明，與TC11鈦合金鍛件相比，連續(xù)點式鍛壓激光快速成形的TC11鈦合金的強度高，而塑性低。斷口形貌分析表明，晶間斷裂是導致TC11鈦合金塑性差的主要原因。

The titanium alloy parts, which have been formed by traditional laser additive manufacturing (LAM) method, usually have obviously different microstructure from wrought microstructure of titanium alloy and show room temperature mechanical anisotropy. In order to make the LAMed titanium alloy parts get the same microstructure and mechanical properties as wrought titanium alloy, a new technology of LAM called consecutive point-mode forging and laser rapid forming (CPF-LRF) has been proposed. During CPF-LRF process, deposited TC11 titanium alloy by laser rapid forming (LRF) was deformed by consecutive point-mode forging (CPF), and then on the surface of the deformed TC11 titanium alloy, new LRF process started over again. Both LRF and CPF were performed alternatively throughout the process of the fabrication of a TC11 titanium alloy part. Microstructures and mechanical properties of the CPF-LRFed TC11 alloy sample have been investigated. The average grain size of equiaxed grains of the CPF-LRFed TC11 alloy sample is 48.7 μm. The equiaxed grains have continuous grain boundary α phase. The microstructure of the equiaxed grain is bimodal microstructure consisting of primary α phase lath and transformed β. During CPF-LRF process, being plastically deformed by CPF, the surface deformation zone of the thick-wall TC11 titanium alloy part is 1.5 mm depth and its deformation degree is 20%. During a new layer deposited on the surface of the CPF cold deformed TC11 titanium alloy part, when laser beam scans through, about 1 mm thick (four layers) cold deformed titanium alloy in the heat affected zone of laser melting pool is heated up above β-transus temperature of TC11 titanium alloy in which static recrystallization complete within time interval of 0.86 s. The mechanical properties indicate that compared with the tensile properties at room temperature of TC11 alloy forged piece, the CPF-LRFed TC11 alloy has higher strength and less ductility. Fracture analysis indicates that intergranular fracture is mainly responsible for the poor ductility of CPF-LRFed TC11 alloy.

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