正常晶粒长大的计算机模拟（I）——晶粒长大动力学跃迁概率的改进

根据晶粒长大真实的物理过程提出了构建跃迁概率所必须满足的条件。在此基础上提出了正确考虑温度影响的跃迁概率，并采用该概率对晶粒长大过程中温度和第二相粒子含量的作用进行了模拟。模拟结果可以更真实地反映晶粒长大的物理过程，又能与已有的计算数据相容，表现出较传统概率更好的优越性。     

过时效工艺对AA2195铝锂合金微观组织的影响

采用扫描电子显微技术（SEM）、透射电子显微技术（TEM）、背反射电子衍射技术（EBSD）等分析手段对AA2195铝锂合金过时效对析出相粒子组态、细晶组织的影响进行了研究。结果表明：时效过程中析出的球状粒子为富Cu相,板条状相为富CuFe相;在相同的时效时间下,越高的处理温度可以得到更大的析出相粒子体积分数;在600K以下时效时,粒子沿原始晶界呈连续分布,并几乎占满所有晶界,这种网状分布的粒子在最终快速退火中不仅无法提供足够的形核位置,还将成为大角度晶界移动的障碍,导致大尺寸扁平状晶粒组织的形成,而600K以上的样品则可以得到球状粒子,晶界上无连续分布的粒子,得到了比较理想的晶粒组织。600K／24h炉冷是AA2195铝锂合金超塑性预处理的最佳时效工艺。     

A SIMULATION STUDY OF THE GROWTH OF THE MINOR PHASE GRAIN IN A DUAL-PHASE METAL

1.IntroductionInaccordancewiththeprincipleofthecanonicalensemble,asystemwithagivenvolumeofV,particlenumberofNandtheenergybetweenEandE aEhasop(E,BE)asitsmicro-stateassemble.Whentheensemblereachestoequilibrium,eachmicro--statewhichbelongstotheassemblegb(E,BE)appearatequalprobabilitylll.Basedonthistheorythepaperdiscussedthegrowthprocessofthesecondaryphasegraillinadualphasemetalattheelevatedtemperaturebynumericalmodel.Whenmetalsareannealedatelevatedtemperatures,crystalgrainsareobservedtogrow.…     

A discrete approach to grain growth based on pair interactions

A discrete 3D model for normal grain growth based on pair interactions is presented where the inhibition effect due to second phase particles is also considered. A probabilistic approach has been adopted to evaluate the contact probability between neighbouring grains and the continuity equation has been reformulated and adapted to the structure of the interactions in a discrete system. The present model predicts a quasi-stationary grain size distribution more symmetrical than that by the analytical mean field theory by Hillert. As expected, its skewness is modified by the presence of inhibition by second phases.It is demonstrated that this new approach represents a valuable alternative to the mean field models even if, at present, it gives only a small improvement in explaining the shape of the quasi-stationary grain size distribution found in experiments.     

退火温度对新型锆合金薄板带材析出相和织构的影响

采用扫描电镜和超高分辨透射电镜,对具有良好冲制性能的新型锆合金薄板成品带材进行含晶粒、第二相粒子等在内的显微组织研究,并探索真空退火处理条件下温度对带材显微组织的影响。结果显示:新型锆合金薄板成品带材晶粒平均尺寸2.17 μm,存在{0001}<1010>和{0001}<1120>两种织构,大部分晶粒<1120>平行带材RD方向,较少晶粒<1010>平行带材RD方向;第二相粒子分布在晶粒内部及晶界,平均尺寸114 nm,尺寸较大的为不规则椭圆形的Zr-Nb-Fe相,尺寸较小的为圆形的β-Nb相;热处理退火温度降低,带材晶粒尺寸减小,第二相粒子细小弥散分布;新型锆合金薄板成品带材良好冲制性能主要源于轧制积累应变诱发再结晶过程进行充分,导致晶粒细小及孪晶发生破碎;相对轧制变形,退火对带材冲制性能影响不显著。     

微量TiC对Mo-Ti-Zr-TiC合金性能与显微组织的影响

采用粉末冶金方法制备Mo-Ti-Zr-TiC合金,研究微量TiC的添加对Mo-Ti-Zr-TiC合金的拉伸性能和显微组织的影响。结果表明,在Mo-Ti-Zr合金中添加微量TiC(0.1%～0.5%,质量分数)后,合金的相对密度和室温抗拉强度得到了提高,当TiC添加量为0.4%时,合金强度最高,较Mo-Ti-Zr合金提高了28.1%。微量TiC的添加,阻碍了合金烧结过程中的晶粒长大,合金晶粒尺寸随TiC添加量的增加而降低。添加的细小TiC粒子在高温烧结过程中或与坯体中的微量氧发生反应形成了由Mo、Ti、C及O4种元素组成的(Mo,Ti)xOyCz细小复合第二相粒子,或发生团聚结成大颗粒,对合金起到净化晶界氧和弥散强化的作用,因而合金的性能相比Mo-Ti-Zr合金有了较明显的提高。     

钢中第二相粒子与铸坯表面裂纹分析

测试了Q345B钢的高温力学性能,鉴别了铸坯裂纹处析出物的类型,研究了含铌Q345钢中第二相粒子固溶析出及晶粒长大的规律,探讨了钢中第二相粒子与铸坯表面裂纹的关系及相应的控制措施。     

TiC的添加对Mo-Ti合金性能与组织结构的影响

采用粉末冶金法,通过在金属Mo中添加TiH2粉末及超细TiC粉末制备Mo-Ti-TiC合金,研究TiC的添加对Mo-Ti合金的拉伸性能和显微组织的影响.结果表明,TiC的添加使Mo-Ti合金的拉伸强度得到有效提高.TiC添加量在0.05%(质量分数)时,合金拉伸强度最高,强度较Mp-Ti合金提高了31.7%.TiC的添加保护了基体中由TiH2颗粒分解脱氢所形成的单质Ti颗粒,降低其氧化程度.添加TiC后,合金内部生成含元素Mp、Ti、O和C的第二相粒子,有效阻止合金晶粒长大,因此,随着合金中TiC含量的增加,合金的晶粒尺寸减小.     

Effect of second phase particles on grain refinement during equal-channel angular pressing of an Al-Mg-Mn alloy

The process of grain refinement under severe plastic deformation was examined in an Al-5.4% Mg-0.5% Mn-0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain interval from 1 to 12 at a temperature of ∼300 °C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al₆Mn particles with an average size of ∼25 nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of ∼0.55 μm evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al₆Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization.     

Grain growth simulation with the second phase particle pinning for heat-affected zone of microalloyed steel welds

The second phase particle dispersed in microaUoyed steel has different effects on grain growth depending on their size and volume fraction of the second phase particles which will change during welding thermal cycles.The particle coarsening and dissolution kinetics model was analyzed for continuous heating and cooling.In addition,based on experimental data,the coupled equation of grain growth was established by introdacing limited size of grain growth with the consideration of the second phase particles pinning effects.Using Monte Carlo method based on experimental data model,the grain growth simulation for heat-affected zone of microalloyed steel welds was achieved.The calculating results were well in agreement with that of experiments.     

Influence of TiC Addition on Properties and Microstructure of Mo-Ti AlloyEI北大核心

Mo-Ti-TiC alloys were fabricated by powder metallurgy process through adding TiH2 powder and ultrafine TiC powder into Mo metal. The influence of the addition of nano-scale TIC particles on the microstructure and tensile properties of Mo-Ti alloy was studied. The results indicate that the tensile strength of Mo-Ti alloy was effectively increased by TiC particles addition. Mo-Ti with 0.05wt% TiC exhibited the highest tensile strength, which is 31.7% higher than that of Mo-Ti alloy. The addition of TiC protects Ti from oxidation, which is produced by decomposition and dehydrogenization of TiH2 particles. The second phase particles containing Mo, Ti, 0 and C in the alloy were formed with TiC addition. The grain size of the alloy decreased with the increase of the TIC content since the second phase particles can inhibit the grain growth.     

低碳微合金Ti-Nb可焊钢中的N及其第二相粒子

研究了系列低碳微合金Ti-Nb可焊钢中的N含量对模拟焊接热影响区(HAZ)高温奥氏体晶粒尺寸和冲击韧度的影响及其第二相粒子的作用.对试样进行了大热输入焊接热模拟,测定了高温奥氏体晶粒尺寸和焊后试样中的冲击韧度值,并用透射电子显微镜萃取复型法观察了典型试样中第二相粒子(Ti,Nb)N的形态及分布特征.结果表明,钢中Ti、N含量及第二相粒子的尺寸和数目与高温奥氏体晶粒尺寸及冲击韧度值具有很好的对应关系;钢中的N由于生成了细小弥散分布的第二相粒子(Ti,Nb)N而细化了高温奥氏体晶粒,改善了焊后韧性.低碳微合金Ti-Nb钢中适宜的含氮量有一个范围.     

Thermal Stability Study of Ultrafine Grained 304L Stainless Steel Produced by Martensitic Process

An ultrafine grain 304L stainless steel with average grain size of about 650 nm was produced by martensitic process. 10 mm as-received sheets were 80% cold rolled in the temperature of ?15 °C and then annealed at 700 °C for 300 min to obtain ultrafine grained microstructure. The results showed that the ultrafine grained 304L steel has yield strength of 720 MPa, tensile strength of about 920 MPa, and total elongation of 47% which is about twice that of coarse grain structure. The effect of annealing temperature (750-900 °C) on the grain growth kinetics was modeled by isothermal kinetics equation which resulted in the grain growth exponent (n) and activation energy for grain growth of 4.8 and 455 KJ/mol, respectively. This activation energy was also compared with those for other austenitic steels to better understanding of the nature of grain growth and atoms mobility during annealing. It was found that activation energy for grain growth is about twice higher than self-diffusion activation energy of austenite that is related to the Zener pinning effects of the second phase particles.     

铸态奥氏体晶粒粗化与热装再加热中晶粒的演化

为了探讨铸坯表层粗大奥氏体晶粒的形成机制,研究了奥氏体晶粒在不同保温条件下的粗化行为。发现由于析出相的影响,高温保温时不同钢种间晶粒生长规律存在差异,且晶粒的进一步粗化在1 250 ℃以下难以有效进行。在此基础上,为了明确装炉温度对加热后奥氏体晶粒结构的影响,对模拟热装再加热过程中的晶粒结构演变进行了试验探究。结果表明,高于珠光体形成温度热装时,轧前奥氏体晶粒结构与冷却前一致;而低于此温度热装时,在奥氏体化后出现大量的新生细小晶粒。后者得到的混晶结构在继续加热至均热温度的过程中发生反常晶粒生长,导致最终组织较冷却前更为粗大。     

固溶工艺对6061铝合金组织和拉伸性能的影响

采用光学显微镜、扫描电镜和拉伸试验等方法,研究了固溶处理工艺对6061铝合金微观组织和力学性能的影响。结果表明,随固溶时间的延长和固溶温度的升高,合金中可溶第二相粒子逐渐溶解,再结晶增强,晶粒细化,合金拉伸性能升高;进一步延长固溶时间和提高固溶温度,合金晶粒粗化,合金强度下降。热处理后残留粗大第二相粒子的多少和合金晶粒大小是影响合金拉伸性能和断口形貌的主要因素。时效工艺为180 ℃×8 h条件下,6061铝合金的最佳固溶工艺为535 ℃×80 min。     

弥散强化对铂基材料拉伸性能的影响

对普通和氧化锆弥散强化的铂基材料分别进行了常温和1000℃高温拉伸试验,用光学和扫描电子显微镜对断口及其附近区域的表面形貌和微观组织结构进行了观测。结果表明,在拉伸实验中弥散强化型铂基材料的抗拉强度和屈服强度高于普通铂基材料;弥散强化型铂基材料断口呈韧窝状,且韧窝中能观察到第二相(氧化锆颗粒)的存在。高温拉伸时,由于氧化锆颗粒的弥散强化作用,降低晶界扩散速度,减缓位错攀移,阻止晶粒长大和晶界滑移,提高了铂基材料的强度。     

蒙特卡罗模拟和实验验证纳米薄膜晶粒生长的厚度效应

利用各向异性的蒙特卡罗方法模拟了纳米薄膜在退火过程中的晶粒生长。模拟结果显示,纳米薄膜的厚度效应并非体现在晶粒生长的整个过程中,而是仅当平均晶粒尺寸达到厚度的0.8～1.2倍时才明显表现出来。为描述这种晶粒生长的动力学过程,需要对Burke方程添加一个与晶粒平均尺寸和薄膜厚度之比相关的因子进行修正。Ni/SiO2纳米多层薄膜晶粒生长的试验结果证明了修正方程的合理性。通过比较溶质拖曳、第二相拖曳和厚度效应的动力学方程,提出了一个更为普遍适用的动力学方程。     

应用元胞自动机模型模拟析出相对材料晶粒长大的影响

为了探讨元胞自动机(CA)方法模拟析出相粒子对材料晶粒长大过程影响的应用,在现有晶粒长大CA模型的基础上,综合应用曲率驱动机制和能量驱动机制,建立了适合于含有析出相粒子材料和具有新转变规则的晶粒长大模型,应用该模型对含有不同体积分数析出相粒子的材料晶粒长大过程进行了仿真模拟和定量分析。结果表明:所建模型能够较准确地反映析出相粒子对晶粒长大过程影响的基本规律,且更加敏感地反映了析出相粒子体积分数对晶粒长大过程的影响;随着析出相粒子体积分数的逐渐增加,晶界脱钉现象不易发生且晶粒长大指数不断减小。     

微观组织对16MnDR钢板韧脆转变温度与无塑性转变温度的影响

韧脆转变温度FATT和无塑性转变温度NDT是评价低温压力容器用钢板低温性能的两个关键指标。利用金相显微镜、扫描电镜、透射电镜和能谱分析仪分析了带状组织、夹杂物、第二相粒子等微观组织对48 mm 厚16MnDR钢板FATT与NDT的影响。研究表明, 该钢板的韧脆转变温度为-40 ℃,无塑性转变温度为-55 ℃,-40 ℃低温冲击功满足标准要求,且富裕量较大,钢板具有良好的低温韧性和低温止裂性。生产时需兼顾铸坯质量、夹杂物、第二相粒子等影响其低温性能的因素,尽量减少夹杂物含量,缩小夹杂物尺寸,避免带状组织的过分粗大及第二相粒子的聚集长大,只有多种影响因素的综合控制,才能保证钢板具有良好的低温性能。     

正常晶粒长大的计算机模拟(Ⅱ)--第二相粒子形状及取向的影响

采用改进的跃迁概率和MonteCarlo加速算法,模拟了第二相粒子不同形状及其取向对基体晶粒长大的影响.模拟结果表明:针状粒子钉轧晶界的效果好于球状粒子,但随着第二相面积分数fA的增加,晶粒平均尺寸受第二相形状的影响逐渐减小,而晶粒形态受到的影响逐渐增强;取向对基体晶粒长大没有明显影响.