累積疊軋TC4鈦合金的組織演化與力學(xué)性能

累積疊軋TC4鈦合金的組織演化與力學(xué)性能MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF TC4 ALLOY DURING ACCULATIVE ROLL BONDING PROCESS

采用累積疊軋技術(shù)進(jìn)行TC4鈦合金超細(xì)晶組織的制備，考察了疊軋工藝對界面結(jié)合和微觀組織的影響規(guī)律以及該過程中α/β兩相鈦合金的變形機(jī)制，獲得了疊軋工藝對TC4合金力學(xué)性能的影響。結(jié)果表明，TC4合金累積疊軋過程中需要足夠的加熱溫度(近于720℃)、防氧化處理以及多層數(shù)大下壓量的軋制工藝，進(jìn)而獲得良好的界面結(jié)合，界面處存在氧含量較高的硬化層。隨著疊軋溫度和疊軋層數(shù)的增加，結(jié)合界面發(fā)生擴(kuò)散、縮頸斷裂并逐漸與基體一致。累積疊軋過程是協(xié)同變形和剪切變形綜合作用的結(jié)果，變形初期晶界β相由長條狀轉(zhuǎn)變?yōu)槎唐瑺钜约熬Ы绨l(fā)生滑移，而在變形程度較高時(shí)組織中存在大量的剪切帶，存在大量局部變形適應(yīng)大塑性變形過程。變形組織中存在局部等軸組織（~300nm）和拉長的變形結(jié)構(gòu)（~400nm），其中等軸組織是由于變形溫度、局部剪切變形和局部過熱作用而發(fā)生再結(jié)晶的結(jié)果。疊軋板材在厚度方向存在組織性能不均勻現(xiàn)象，在結(jié)合界面處硬度值較高，隨著疊軋層數(shù)的增加硬度值逐漸趨于一致。同時(shí)隨疊軋層數(shù)增加強(qiáng)度逐漸增加，在疊軋16層后抗拉強(qiáng)度達(dá)到1325MPa，同時(shí)塑性降低為5.4%。在疊軋層數(shù)較少時(shí)斷裂過程表現(xiàn)為韌性斷裂，隨著疊軋層數(shù)的增加界面逐漸轉(zhuǎn)變?yōu)轫g窩斷口和準(zhǔn)解理斷口的綜合形貌。

The accumulative roll-bonding (ARB) was conducted for the ultra-fine grains of TC4 titanium alloy, and the effect of the ARB temperature and cycles on the bonding interface and microstructure was investigated as well as the deformation mechanism of the mixed α/β phase structure, and finally the mechanical properties were obtained for the ARB processed TC4 alloy. The proper ARB temperature (~720℃)，the anti-oxidation treatment and the multilayer with the high deformation for the interface bonding should be taken, which always takes on the hardened interface with the high oxidation contents, and the interface bonding strength increases with the increase of the ARB layers and temperature through the process of the diffusion and the necking fracture. The deformation process is composed by the cooperation deformation of α/β structure and the shear deformation during ARB processed TC4 alloy, during which the β phase at the grain boundary changes from the long strips to the short bands to deform with hcp α phase, while the shear bands with the severe local-deformation is used to adapt the severe plastic deformation. The deformed microstructure is composed of the equiaxed structure (~300nm spacing) and the elongated deformation structure (~400nm spacing), in which the equiaxed structure comes from the function of the deformation temperature, local shear deformation and the local overheat. Additionally, the inhomogeneous microstructure and properties along the thickness direction can be observed, and the high hardness values can be obtained at the bonding interface, which gradually distributes homogeneous with the increase of the ARB layers. The strength of the ARB processed TC4 sheets increases with the increase of the ARB layers, which can get to 1325MPa after 16 ARB layers, and simultaneously the plastic decrease to 5.4%. The ductile fracture can be observed with the low ARB layers, while the mixed structure of the quasi-cleavage and ductile fracture is obtained with the increase of the ARB layers.

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