(1. 重慶理工大學(xué) 機(jī)械工程學(xué)院，重慶 400054；
2. 四川大學(xué) 建筑與環(huán)境學(xué)院，成都 610065)
摘 要: 采用分子動(dòng)力學(xué)方法研究了微觀尺度下晶粒尺寸和冷卻速率對(duì)NiTi合金相變溫度的影響和相變微觀機(jī)理。結(jié)果表明：當(dāng)冷卻速率為-5 K/ps，晶粒尺寸從17.5 nm減小到8.1 nm時(shí)，馬氏體相變起始溫度從230 K下降到80 K，馬氏體相變形核點(diǎn)的數(shù)目逐漸減少且主要出現(xiàn)在晶粒內(nèi)部，降溫過(guò)程中馬氏體相成核后向晶界處擴(kuò)散生長(zhǎng)，當(dāng)晶粒尺寸減小至4.1 nm時(shí)，馬氏體相變效應(yīng)則受到抑制；而升溫過(guò)程中，奧氏體相變形核點(diǎn)主要出現(xiàn)在晶界處，且隨著溫度的升高，形核點(diǎn)主要向晶粒內(nèi)部聚集生長(zhǎng)。當(dāng)冷卻速率從-5 K/ps增加到-15 K/ps，晶粒尺寸為17.5 nm的模型中馬氏體相變結(jié)束溫度從190 K減小到20 K。隨著冷卻速率的增加，馬氏體晶粒細(xì)化程度相應(yīng)增加，相變滯后寬度(Mf-Af)隨著冷卻速率的增加相應(yīng)增大，但是冷卻速率對(duì)馬氏體相變生長(zhǎng)機(jī)制影響相對(duì)較小。
關(guān)鍵字: 形狀記憶合金；相變溫度；冷卻速率；分子動(dòng)力學(xué)
（1. College of Mechanical Engineering, Chongqing University of Technology, Chongqing, 400054, China;
2. School of Architecture and Environment, Sichuan University, Sichuan, 610065, China）
Abstract:The molecular dynamic simulation was conducted to analyze the influence of grain size and cooling rate to the phase transformation temperature, and the phase transformation mechanism for the alloy was also studied. The result shows that when the cooling rate is -5 K/ps, as the grain size decreases from 17.5 nm to 8.5 nm, the martensite formation temperature decrease from 230 K to 80 K, the number of nucleation point also decreases gradually and only nucleate inside the grain, the martensite grows towards the grain boundary in the process of cooling. When the grain size decreases to 4.1 nm, the transformation is suppressed. In the process of heating, the nucleation point of austenits nucleates near the grain boundary and grows towards inside of the grain. When the cooling rate increases from -5 K/ps to -15 K/ps, the finish transformation temperature of martensite decreases from 190 K to 20 K, the grain refinement increases and the transformation hysteresis width (Af-Mf) decreases with the increase in cooling rate in the model of 17.5 nm. While the effect of cooling rate on martensitic phase growth mechanism is relatively small.
Key words: shape memory alloy; phase transformation temperature; cooling rate; molecular dynamics
