热轧Nb-Ti-V钢应变诱导析出动力学的计算模型

以规则溶液亚点阵模型和经典型核长大理论为基础，计算了Nb-Ti-V复合微合金化钢的应变诱导析出动力学．计算所得的析出-时间-温度（PTT）曲线与采用等温应力松弛法所获得的实验结果基本符合。     

可控电磁能(CEME)时效处理下Al-Zn-Mg-Cu合金的析出及强化机理研究

文中提出了可控电磁能(CEME)铝合金辅助时效处理技术,研究了脉冲电磁场产生的可控电磁能对Al-Zn-Mg-Cu合金析出相密度、尺寸分布及力学性能的影响并分析了组织强化机制.引入磁-热扩散模型和量子力学探讨外加脉冲磁能作用下Al-Zn-Mg-Cu合金的扩散析出机理.结果表明,施加脉冲电磁场有利于增加析出质点数量,而延长时效可促进析出相长大,经脉冲电磁场时效1 h后的析出相分布密度为1.124μm-2,约为传统时效12 h的3倍,其抗拉强度分别为506 MPa和542 MPa;随着析出相尺寸的增大,强化机理由共格应变场强化机制(OS)过渡至Orowan绕过强化模型(CS),理论临界析出颗粒尺寸为20 nm.动力学分析认为,外加磁能对扩散激活能的Gtot作用较小,提高原子振动频率v0是增加析出质点数量的主要原因.     

23Cr-14Ni高氮奥氏体不锈钢σ相析出行为EI北大核心CSCD

采用经验公式、热力学计算方法、Gleeble热/力模拟实验技术,结合光学显微镜、扫描电镜及透射电镜分析,研究了23Cr-14Ni高氮奥氏体不锈钢中σ相的析出行为。结果表明,23Cr-14Ni高氮奥氏体不锈钢中σ相可在960~1030℃析出,高于1050℃溶解。σ相析出具有异常快速的动力学特征,在经过1030℃保温1 min固溶处理后,σ相可直接从奥氏体晶界快速析出,析出先于碳氮化物相。σ相析出动力学行为及相对碳氮化物的析出次序和传统奥氏体不锈钢显著不同。铬、锰、钼元素含量较高且钼元素在晶界处偏聚提高了σ相平衡析出温度,是加速σ相析出的主要原因。     

Nb微合金钢析出行为的热力学计算

以析出热力学为基础，对Fe-Nb-C-N系统中奥氏体／碳氮化物的热平衡过程，计算了不同温度下碳氮化物析出相的平衡摩尔分数、化学驱动力、各组元的原子分数及奥氏体组分等．结果表明，随着温度的降低，析出相的平衡摩尔分数增大，溶解在奥氏体中的各组元的摩尔分数降低，析出相的化学驱动力增大．在低温条件下，Nb和N元素巳基本析出．碳化物在析出物中所占的比例主要取决于钢的成分和温度．对于同一成分的钢种，这一比值随着温度的降低而增大．     

Nb含量对625合金带极堆焊层耐晶间腐蚀性能的影响

研究了不同Nb含量对625合金带极堆焊金属的组织转变及耐晶间腐蚀性能的影响。结果表明,Nb含量的增加导致堆焊层耐腐蚀性能显著下降。Nb含量较低时,合金中析出相以MC为主,Laves相很少,具有较好的耐腐蚀性能。Nb含量增加后,在枝晶间产生强烈偏析,促进合金中富Nb、Mo、Si的Laves相的析出和长大。块状形态的Laves相本身贫铬并造成枝晶间区域较大的成分差异,导致析出相附近成为晶间腐蚀的薄弱区,明显加快合金的腐蚀速率。     

Mg-10Gd-3Y-0.5Zr合金热压缩动态析出规律

本文定量地研究了Mg-10Gd-3Y-0.5Zr(GW103K)合金在350℃~450℃及10~(-4)s~(-1)~10~(-1)s~(-1)热压缩条件下的动态析出规律。结果表明:固溶处理后的合金在450℃下压缩时,晶内和晶界均无析出相产生,在350℃~400℃热压缩时,有大量不规则颗粒状的析出相产生;析出相主要是β相,平均成分为Mg5.5(Gd_(0.73)Y_(0.27)),大部分分布于再结晶小晶粒的晶界处;析出相的尺寸随温度升高和应变速率的降低而增大,400℃、10~(-4)s~(-1)变形条件下的析出相尺寸能达到1μm以上,而350℃、10~(-4)s~(-1)变形条件下的析出相尺寸在100nm左右;析出相的体积分数随应变量呈非线性增加。不同的变形条件下,析出相体积分数增长趋势不同。350℃下的析出相体积分数在应变量为1.10时达到了3.5%。热压缩过程中,动态析出阻碍位错运动,抑制再结晶晶粒长大,对细化再结晶晶粒起到重要作用。     

预应变对Nb微合金化09MnNiDR低温钢高温塑性的影响

利用光学和电子显微镜观察断口组织,并测定断面收缩率来研究预拉伸应变对Nb微合金化低温钢09MnNiDR高温塑性的影响。当试样进行5%变形量预拉伸,800℃时断口组织主要为铁素体,晶界处有网状先共析晶界铁素体,断面收缩率为63%;900℃时断口组织主要为贝氏体和针状铁素体以及大量碳氮化物,断面收缩率降至35%;1000℃时断口组织主要为板条马氏体,断面收缩率升至95%。与未进行预应变试样相比,在800～920℃的温度区间,断面收缩率显著降低,预应变明显恶化了Nb微合金化09MnNiDR钢的高温塑性,这主要与预应变促进了尺寸为十几纳米至几十纳米Nb碳氮化物的沿晶界析出有关。     

铌硼微合金钢高温应变诱导析出行为

用应力弛豫方法研究了超低碳铌硼微合金钢在８００℃，８５０℃、９００℃和９５０℃下，经过２０％预变形目的等温应变诱导析出行为。样品的透射电镜观察表明：应变诱导析出只在位错线上形核并阻碍位错运动，而位错一旦摆脱钉扎，这种运动位错可以是样品中进一步析出的优先形核位置，从而导致析出分阶段进行。     

含Zr、Sc的Al-Zn-Mg-Cu合金的低周疲劳行为

利用透射电子显微镜和低周疲劳试验机研究了单级时效状态及回归再时效状态两种含Zr、Sc的Al-Zn-Mg-Cu合金的微观组织和低周疲劳性能。结果表明:单级时效基体析出相以η′相为主,晶界析出连续分布平衡相,并伴有晶间无析出带;回归再时效基体析出相略有长大,晶界析出相长大明显,无析出带变宽。低周疲劳加载条件下,合金在0.4%~0.7%外加总应变幅范围内表现出循环稳定性;在0.8%的应变幅下,呈现先软化后硬化。在0.4%~0.6%较低的外加总应变幅范围内,回归再时效合金表现出较高的低周疲劳寿命。两种状态合金的塑性应变幅和弹性应变幅与载荷反向周次之间均成直线关系,并可分别用Coffin-Manson公式和Basquin公式来描述。两种状态的合金的疲劳裂纹均萌生于试样表面,并以穿晶方式扩展。     

α区形变对微合金钢中析出相和强度的影响

采用Gleeble热模拟实验机对含Nb、Mo微合金钢进行了铁素体(α)区形变+等温工艺实验,研究了微合金钢中析出相的变化及其对强度的影响。利用透射电镜对不同工艺所制备试样中析出相的形貌进行观察和分析,纳米级析出相弥散分布于铁素体基体之中;并对析出相的尺寸进行统计分析,结果表明,相较于等温工艺,形变+等温工艺可以明显细化析出相的尺寸,且在600 ℃下获得的析出相尺寸更为细小,平均尺寸为2.77 nm。利用Thermo Calc数据库计算平衡条件下600和700 ℃时(Nb1-xMo_x)C中的x值和析出相的体积分数,结合实验中统计的析出相尺寸,分析了不完全析出条件下(Nb1-xMo_x)C析出相对屈服强度的贡献。结果表明,在600 ℃进行形变+等温工艺,尽管析出相的体积分数不高,但因 (Nb1-xMo_x)C的尺寸更小,其提供的屈服强度增量更高。     

Strain-Induced Precipitation Kinetics of Vanadium Carbonitride Precipitates with the Cubic Structure in High-Strength Weathering Steels

Strength of Materials - The strain-induced precipitation kinetic model of vanadium carbonitride [V(C, N)] precipitates with the cubic structure in vanadium-nitrogen (V–N) microalloyed...     

Unraveling the origin of strain-induced precipitation of M23C6 in the plastically deformed 347 Austenite stainless steel

In this research, the phenomenon of strain-induced precipitation of M₂₃ (M = Cr, Fe, Mo) C₆ precipitates in 347 austenite stainless steel was systematically studied. During annealing at 650 °C, the experimental results exhibited significantly earlier formation of M₂₃C₆ precipitates in the plastically strained specimen, than in the no-strain specimen. The various microstructural characterizations showed that the accelerated formation of M₂₃C₆ precipitates occurred around deformation bands that were generated by deformation twinning. Extensive investigation suggested that the strain-induced precipitation of M₂₃C₆ is attributed to the formation of strain-induced α′ martensite during plastic deformation near deformation bands.     

Effect of V and V-N Microalloying on Deformation-Induced Ferrite Transformation in Low Carbon Steels

Deformation-induced ferrite transformation （DIFT） has been proved to be an effective approach to refine ferrite grains. This paper shows that the ferrite grains can further be refined through combination of DIFT and V or V-N microalloying. Vanadium dissolved in γ matrix restrains DIFT. During deformation, vanadium carbonitrides rapidly precipitate due to strain-induced precipitation, which causes decrease in vanadium dissolved in matrix and indirectly accelerates DIFT. Under heavy deformation, deformation induced ferrite （DIF） grains in V microalloyed steel were finer than those in V free steel. The more V added to steel, the finer DIF grains obtained. Moreover, the addition of N to V microalloyed steels can remarkably accelerate precipitation of V, and then promote DIFT. However, DIF grains in V-N microalloyed steel easily coarsen.     

Revealing Precipitate Development During Hot Rolling and Cooling of a Ti–Nb Micro-Alloyed High Strength Low-Alloy Steel through X-Ray Scattering

High-energy synchrotron X-ray small-angle scattering (SAXS) is used to study the precipitate development during hot rolling and cooling of a commercial Ti–Nb micro-alloyed, high-strength, low-alloy (HSLA) steel. To study precipitation during hot rolling conditions, Gleeble and dilatometer trials are made. Samples are then studied at room temperature using SAXS in conjunction with transmission electron microscopy (TEM). TEM is used to determine the morphology and composition of the precipitates, whilst both TEM and SAXS are used to study the particle sizes. One major advantage with high-energy SAXS is the ability to make measurements after a minimum of sample preparation and in transmission geometry, as opposed to just at prepared surfaces, plus the possibility to determine volume fractions of the precipitates. The measurements show that after deformation at high temperature, particle coarsening occurs and the volume fraction of precipitates increases after holding for 20 s at 900 °C which confirms strain-induced precipitation at finishing rolling conditions. The measurements show that holding at 600 or 650 °C for one hour gives a larger volume fraction of nanosized particles. Coiling simulations with slow cooling from 600 to 470 °C show coarsening of particles and an increase in the volume fraction of the smaller particles compared to holding at a constant temperature.     

Investigation of the effect of Al-8B master alloy and strain-induced melt activation process on dry sliding wear behavior of an Al–Zn–Mg–Cu alloy

This study was undertaken to investigate the influence of Al–8B master alloy and modified strain-induced melt activation process on the structural characteristics and dry sliding wear behavior of Al–12Zn–3Mg–2.5Cu aluminum alloy. The optimum amount of B containing master alloy for proper grain refining was selected as 3.75 wt.%. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The optimum temperature and time in strain-induced melt activation process are 590 °C and 10 min, respectively. T6 heat treatment was applied for all specimens before wear testing. Significant improvements in wear properties were obtained with the addition of grain refiner combined with T6 heat treatment. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3 Mg–2.5Cu aluminum alloy to the dry sliding wear. The results showed that dry sliding wear performance of globular microstructure specimens was a lower value than that of B-refined specimens without strain-induced melt activation process.     

New observations on the formation of strain-induced martensite in an Fe-29.6%Ni alloy

Observations of the morphology and substructure of strain-induced martensites in an Fe-29.6%Ni alloy revealed the formation of butterfly- and lath-like transformation products with {11 NJ2}_b <111>_b type transformation twins and a parallel array of straight screw dislocations along <111>_b directions depending upon the amount of plastic deformation. Crystallographic analysis showed the formation of strain-induced martensites with unique {225}_f habit plane and a Kurdjumov—Sachs-type orientation relationship relative to the matrix austenite at least up to the large deformation ranges which could easily make the Crystallographic measurements unfeasible. It has been shown that the strain-induced martensites are formed with more elongated shapes as the amount of plastic deformation is increased.     

Strain-induced magnetization of amorphous ferromagnets

The magnitude of the strain-induced magnetization (ΔB _σ effect) of a Fe_81.5B_13.5Si₃C₂ amorphous ferromagnetic alloy was studied as a function of the applied magnetic field, the frequency of alternating elastic stress, and the thermomagnetic treatment temperature. It is shown that processes involved in the strain-induced magnetization of the alloy studied are determined by the frequency of alternating elastic stress and the thermomagnetic treatment temperature.     

Significantly enhanced the ductility of the fine-grained Al–Zn–Mg–Cu alloy by strain-induced precipitation

A fine-grained structure of Al–Zn–Mg–Cu alloy was produced by a successive two-step deformation (STD) process based on strain-induced precipitation (SIP). The fine-grained alloy treated by the STD process exhibited significantly superior tensile ductility than the conventional hot-deformed (CHD) alloy. Effects of the STD process on microstructure and mechanical properties were investigated, in conjunction with fracture characterizations. Numerous spherical precipitates and dense dislocations were induced by the SIP at 300 °C. A fine lamellar structure was formed during subsequent heating and hot deformation of the STD process, finally contributing to the fine-grained T6-aged alloy. Due to the fine-grained structure, more dimples in the fracture surface of the STD treated alloy were produced than those of the CHD treated alloy. TEM in-situ testified that the grain boundary precipitates (GBPs) originated the initiation of micro-cracks, and the cracks propagated along the (sub)grain boundaries during the tensile loading. The initiation and propagation of micro-cracks were explained in terms of grain boundary precipitates (GBPs), precipitation free zones, and grain refinement. Although initiation and propagation of the cracks easily occur to coarse GBPs and grain boundaries, the fine-grained structure obtained by the STD treatment could effectively delay these behaviors and improve mechanical properties.     

X-ray Diffractions of Deformation Structure in Polycrystalline Fe-32Mn-5Si Alloy

The change of microstructure with strain was investigated in a Fe-32Mn-5Si austenitic alloy at room temperature by X-ray diffraction profile analysis. The experimental results show that the Fe-32Mn-5Si alloy is deformed by the strain-induced γ→ε transformation and the twinning except dislocation slip at room temperature. The amount of strain-induced ε-martensite, the stacking fault probability and the twinning probability all exhibit parabolic relationship with increasing strain. The stacking fault probability is higher than the twinning probability.     

Kinetic vs. strain-induced growth instabilities on vicinal Si(001) substrates

The vicinal Si(001) surfaces are known to exhibit both kinetically and thermodynamically driven instabilities during overgrowth with Si or SiGe. Here, we present a comparative study that allows the discrimination of kinetic effects and strain-induced equilibrium effects. Under kinetic growth conditions, layers with low Ge content become smoother than their homoepitaxial Si counterparts. In contrast, for layers with high Ge content, hut cluster formation is identified as the dominant mechanism of the epilayer to relax strain. We find no evidence for one-dimensional strain-induced step bunching on small angle miscut substrates. Our results strongly suggest that kinetic or kinetically limited processes rather than thermodynamic effects determine the morphology of Si/SiGe interfaces at 550°C.