(1. 西安交通大學(xué) 機(jī)械工程學(xué)院，西安 710049；
2. 西安交通大學(xué) 機(jī)械制造系統(tǒng)工程國(guó)家重點(diǎn)實(shí)驗(yàn)室，西安 710049)
摘 要: 采用分子動(dòng)力學(xué)方法模擬不同孿晶密度和不同溫度下納米孿晶鈦單軸拉伸力學(xué)行為。模擬結(jié)果表明：室溫下隨著孿晶密度的降低，納米孿晶鈦的屈服強(qiáng)度出現(xiàn)先提升后降低的現(xiàn)象，材料存在臨界孿晶密度。當(dāng)孿晶密度小于臨界孿晶密度時(shí)，孿晶界對(duì)晶粒的細(xì)化作用導(dǎo)致材料的強(qiáng)度提升。當(dāng)孿晶密度大于臨界孿晶密度時(shí)，孿晶界、晶界和兩者交匯處的位錯(cuò)成核增殖成為材料變形的主導(dǎo)因素；且當(dāng)孿晶密度遠(yuǎn)離臨界值時(shí)，孿晶間隔變小、位錯(cuò)源增多，位錯(cuò)成核與增殖加劇，材料的強(qiáng)度降低。相同孿晶密度條件下，晶粒尺寸的減小會(huì)減少晶粒內(nèi)孿晶界的數(shù)量，進(jìn)而減少孿晶和晶界交匯處位錯(cuò)源的生成，增強(qiáng)了屈服強(qiáng)度。此外，溫度的變化會(huì)影響原子的活躍程度和晶格的變形機(jī)制。隨著溫度的升高，原子間結(jié)合力下降，晶界附近原子結(jié)構(gòu)無序化和HCP-BCC相變程度加劇引起材料的彈性模量、屈服強(qiáng)度下降，同時(shí)位錯(cuò)形核與運(yùn)動(dòng)的加劇影響了材料的塑性變形。
關(guān)鍵字: 納米孿晶鈦；孿晶密度；位錯(cuò)；溫度；分子動(dòng)力學(xué)
（1. School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, China;
2. State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China）
Abstract:The mechanical behavior of nano-twinned titanium under uniaxial tension was simulated by molecular dynamics at different twin densities and temperatures. The simulation results show that with the decrease of twin density, the yield strength of nano-twinned titanium first increases and then decreases at room temperature, and there is a critical twin density in the material. When the twin density is less than the critical twin density, the grain refinement effect of twins leads to the increase of the strength of the material. When the twin density is larger than the critical twin density, the nucleation and increment of dislocations at twin boundary, grain boundary and their intersection become the dominant factors of material deformation, which affect the mechanical properties of nano-twinned titanium. When the twin density is far away from the critical value, the twin spacing becomes smaller, the nucleation and proliferation of dislocations become more intense, and the strength of the material decreases. The change of temperature can affect the activity of atoms and the deformation mechanism of lattice. With the increase of temperature, the bonding force between atoms decreases, the disorder of atomic structure near the grain boundary and the degree of HCP-BCC phase transformation increase, resulting in the decrease of elastic modulus and yield strength, and the increase of dislocation nucleation and movement affects the plastic deformation of the material.
Key words: nano-twinned titanium; twin density; dislocation; temperature; molecular dynamics
