(1. 西安交通大學 機械工程學院，西安 710049；
2. 西安交通大學 機械制造系統(tǒng)工程國家重點實驗室，西安 710049)
摘 要: 采用分子動力學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行為。模擬結果表明：室溫下隨著孿晶密度的降低，納米孿晶鈦的屈服強度出現(xiàn)先提升后降低的現(xiàn)象，材料存在臨界孿晶密度。當孿晶密度小于臨界孿晶密度時，孿晶界對晶粒的細化作用導致材料的強度提升。當孿晶密度大于臨界孿晶密度時，孿晶界、晶界和兩者交匯處的位錯成核增殖成為材料變形的主導因素；且當孿晶密度遠離臨界值時，孿晶間隔變小、位錯源增多，位錯成核與增殖加劇，材料的強度降低。相同孿晶密度條件下，晶粒尺寸的減小會減少晶粒內孿晶界的數(shù)量，進而減少孿晶和晶界交匯處位錯源的生成，增強了屈服強度。此外，溫度的變化會影響原子的活躍程度和晶格的變形機制。隨著溫度的升高，原子間結合力下降，晶界附近原子結構無序化和HCP-BCC相變程度加劇引起材料的彈性模量、屈服強度下降，同時位錯形核與運動的加劇影響了材料的塑性變形。
關鍵字: 納米孿晶鈦；孿晶密度；位錯；溫度；分子動力學
（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
