WC_p/B_4C_p/6063Al复合材料的预形变热处理

采用粉末冶金工艺制备了WCp/B4Cp/6063Al复合材料,通过SEM和XRD对复合材料的显微组织进行了表征,研究了预形变热处理工艺对复合材料力学性能的影响。结果表明,当形变量超过某临界值时,复合材料经过预形变热处理可以实现很好的强化效果;本实验中当挤压比达到或超过15∶1,热处理温度为520℃时,复合材料经过预变形热处理获得了最佳的力学性能。断口表面形貌分析表明,预形变热处理后基体合金的强化是复合材料整体力学性能提高的根源。

预形变量和半固态等温温度对触为组织的影响

研究了预形变量与半固态等温温度对应力诱发熔化激活（Ｓｔｒａｉｎｉｎｄｕｃｅｄｍｅｌｔａｃｔｉｖａｔｅｄ）工艺所获得的触交组织的影响。结果表明，增加预形变量和半固态等温温度，都将促进合金中初生α相由树枝晶向颗粒状转化。但预形变量过大或半固态等温温度过高，都会使晶粒长大。因此，要获得均匀细小的触变组织，必须使预形变量和半固态等温温度有一个合理的匹配。

预形变和时效Al-2.73Li合金的断裂机制

本文研究了预先冷形变对Al-2.73Li合金的机械性能和断裂行为的影响。试验结果表明,预先冷形变使合金的加工硬化率和强度提高,相应损失部分塑性。预先冷形变造成不均匀分布的胞状位错结构及晶界无沉淀带加工硬化,乃是导致塑性下降的主要原因。合金的断裂方式为沿晶和穿晶混合型。预形变后时效使沿晶断裂倾向增大。最后探讨了其断裂机制。

预形变对2091合金应力腐蚀抗力的影响

研究了预形变和时效对2091合金抗应力腐蚀性能的影响.结果发现,合金在预冷轧1%,并经170℃×5h的时效后不仅具有较高的强度,而且伸长率出现峰值,同时具有最佳的应力腐蚀抗力.对各种状态的合金进行了微观组织分析.

预形变和快速加热对钢淬火组织的影响

对不同预形变量钢材的高温快速加热淬火组织进行了研究，发现钢的组织转变时间随形变量增加而缩短，淬火组织随形变量的增加而细化，形变量超过一定的值后，延长加热保温时间，得到的淬火组织仍较细小。

基于预形变热处理对GH4169蠕变性能影响的研究

研究GH4169在冷拔量14%、20%和冷拔后930℃退火10min对比直接时效的母材蠕变寿命的变化规律,通过观察预形变热处理后的基体表面、蠕变后表面和断口形貌,分析不同预形变热处理下蠕变性能。实验结果表明,冷拔形变后930℃退火10min比冷拔后直接时效的合金具有更高的蠕变寿命,且蠕变寿命都高于直接时效后的母材。冷拔形变和冷拔后进行退火处理的合金蠕变断口都出现大量深浅不一韧窝,韧窝密度随着冷拔量增加呈递增趋势。同一冷拔量和试验条件下,退火处理后的韧窝排列最密集。分析发现,韧窝是晶界空洞形核产生的,空洞吸收蠕变产生的大量能量,延长合金蠕变寿命,提高合金蠕变性能。

疲劳及拉伸预形变对纯铜应力腐蚀敏感性的影响

用慢应变速率拉伸法研究了疲劳预形变以及拉伸预形变对纯钢在ＮａＮＯ２溶液中应力腐蚀敏感性的影响.结果表明，疲劳预形变（切应力幅γｐｌ＝１.２×１０－４，疲劳周次Ｎ＝８．４×１０４；以及γｐｌ＝９．４×１０－４； Ｎ＝２．４×１０４）能降低Ｃｕ单晶的应力腐蚀敏感性．随拉伸预形变量升高，纯铜多品的应力腐蚀敏感性也降低.这表明，预形变能改善纯铜的应力腐蚀性能．

预形变对Ti-9148合金时效过程中相变的影响

医用Ti-9148合金(Ti-19Nb-1.5Mo-4Zr-8Sn)通过真空自耗式电弧炉制备,并经过X射线衍射以及时效硬化曲线分析,研究了预形变对Ti-9148合金时效过程中相变的影响。研究结果表明:预形变对Ti-9148合金的时效硬度变化敏感。其时效硬度随时效温度升高及冷预形变的减小而减小。Ti-9148合金在873 K的相变过程为:β+α'→α+α"+β→α+β。预形变越大,这个相变过程的速度越快,且在时效30 min时,其相转变趋于完成。

预拉伸形变对VIRALL复合板疲劳性能的影响

研究了预拉伸形变对ＶＩＲＡＬＬ复合板疲劳性能的影响，发现疲劳寿命随预形变量的增大而延长对复合板片层中内应力的分析结果表明。

热暴露对表面预形变单晶合金组织和性能的影响

针对[001]取向的DD11单晶合金,在垂直于[001]方向进行2种强度的铸钢弹丸喷丸强化以引入表面预形变,采用电子背散射衍射(EBSD)、扫描电镜和硬度测试等方法研究了预形变后表层组织;后续不同温度热暴露完成后,采用扫描电镜和硬度计,研究了热暴露温度和预形变程度对表层组织和硬度梯度的共同影响;并且表征了喷丸+热暴露后单晶合金的高温疲劳性能。结果表明,单晶合金喷丸预形变后表面出现[110]和[111]取向的亚晶,同时出现表面应变硬化效果;随着形变程度的增大,亚晶取向角、旋转亚晶层深度和硬化效果也随之增大。随着热暴露温度升高,预形变表面形变组织呈现球化-零星不连续胞状组织-连续胞状组织-再结晶的动态回复过程,硬化效果也随之松弛;形变程度越大,开始出现动态回复过程的温度越低,但喷丸+1060℃/2 h热暴露并未观察到再结晶。相比磨削状态,喷丸+热暴露后,1060℃轴向疲劳寿命有所提高。1060℃/350 MPa/R=–1/轴向疲劳源呈现内部萌生为主源,表面为次源的状态。

Strengthening mechanism of T8-aged Al-Cu-Li alloy with increased pre-deformation

The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.

18—8型奥氏体不锈钢形变离子渗氮

本文研究１８－８型奥氏体不锈钢预先形变后再离子渗氮，其预形变的温度、形变度对渗氮层表面硬度、渗层厚度及渗层上氮浓度分布等的影响。研究结果表明：预先室温形变形成以孪晶为主的亚结构，而预先温变形则形成以胞状结构为主的亚结构，不同位错组态的亚结构对氮原子扩散起着不同的作用，致使２００℃预形变的试样离子渗氮后可获得最厚的渗氮层。Ｘ射线衍射分析、极化曲线和点蚀电位测定证明经各种预形变的试样。

预拉伸形变对Mg-Zn-Sr-Zr-Mn合金降解行为的影响

镁合金具有优异的生物相容性和独特降解性,但其在生理环境中的耐蚀性能较差,严重制约了其在临床应用中的发展。使用预拉伸工艺制备Mg-Zn-Sr-Zr-Mn新型镁合金,通过XRD、OM和SEM探究预拉伸形变量与显微组织、腐蚀速率和膜层形貌间的关系。结果表明:随预拉伸形变量的增大(2%、4%、6%),合金晶粒尺寸被逐渐拉长,孪晶数目逐渐增多,析出相离散程度逐渐增大。4%预拉伸合金由于适量孪晶的出现及析出相离散程度的增大,增加了电偶腐蚀形核点位,加速了合金表面均匀氧化产物的快速产生,增大了合金极化电阻阻值;3种预拉伸合金电化学(0.38、0.25、0.74 mm·a^(-1))及失重速率(2.85、1.83、5.88 mm·a^(-1))均呈现先降低后升高的趋势。4%预拉伸合金具有较高的耐蚀性证明适当的预拉伸变形能提高界面析出相的连续性,阻碍腐蚀进程,对合金耐腐蚀性能起到积极作用。而当预拉伸形变量继续增加,产生大量位错,创造氢扩散路径,有利于氢富集,导致合金耐蚀性下降。此外,适当的预拉伸形变通过改变残余应力的重新分布,提高腐蚀均匀性,同时提高膜层致密性与连续性,延缓腐蚀进程。

2091合金的显微组织与应力腐蚀敏感性

用慢应变速率拉伸试验研究不同热处理状态Al—Li—Cu—Mg—Zr(2091)合金的应力腐蚀敏感性,用透射电镜观察显微组织结构并分析变形特性。结果指出,T_2相在晶界上的复盖程度及T_2相之间的平均间距是影响合金应力腐蚀敏感性的主要因素,室温预形变处理可减少晶界上T_2相的数量,使合金应力腐蚀抗力得到明显提高。

Effect of thermo-mechanical treatment process on microstructure and mechanical properties of 2A97 Al-Li alloy

2A97 Al-Li alloy was processed by thermo-mechanical treatment at different pre-stretch deformations of 0, 3% and 6%. The microstrucatre observation results reveal that some δ＇ and T1 precipitates are found in a（Al） matrix of 2A97 alloy processed by the heat treatment with no pre-stretch deformation. When the pre-stretch deformation is 3% and 6%, respectively, amounts of tiny T1 and a few of S＇ precipitates precipitates are observed in the microstructures of 2A97 alloy. The tensile test results show that the tensile properties of 2A97 alloys are improved via thermo-mechanical treatment. When the pre-stretch deformation is from 0, 3% to 6%, the ultimate tensile strength values of the 2A97 alloys increase gradually from 447.7, 516.5 to 534.3 MPa, and the elongations decrease from 17.6%, 12.8% to 10.2%, respectively. Moreover, with increasing pre-stretch deformation amount from 0 to 6%, the in-plane anisotropy value of 2A97 alloys becomes more obvious.

Effect of pre-deformation on aging creep of Al-Li-S4 alloy and its constitutive modeling

A set of uniaxial tensile creep tests at different pre-deformations, aging temperatures and stress levels were carried out for Al-Li-S4 alloy, and the creep behavior and the effects of pre-deformation on mechanical properties and microstructures were determined under basic thermodynamics conditions of aging forming. The results show that pre-deformation shortens the time of primary creep and raises the second steady-state creep rate. Then, the total creep strain is greater, but in the range of test parameters it is still smaller than that without pre-deformation. In addition, transmission electron microscopy（TEM） observation shows that pre-deformation promotes the formation of T1 phase and θ′ phase and makes them distribute more dispersively, while inhibits the generation of δ′ phase, which leads to the improvement of mechanical properties of the alloy. A unified constitutive model reflecting the effects of aging mechanism, stress levels and different pre-deformations was established. The fitting results agree with the experimental data well.

Effect of pre-deformation on microstructures and mechanical properties of high purity Al-Cu-Mg alloy

The effects of pre-deformation following solution treatment on the microstructure and mechanical properties of aged high purity Al-Cu-Mg alloy were studied by tensile test, micro-hardness measurements, transmission electron microscopy and scanning electron microscopy. The micro-hardness measurements indicate that compared with un-deformed samples, the peak hardness is increased and the time to reach peak hardness is reduced with increasing pre-strain. Additionally, a double-peak hardness evolution behavior of cold-rolled （CR） samples was observed during aging. The results of TEM observation show that the number density of S′（Al2CuMg） phase is increased and the size is decreased in CR alloy with increase of pre-strain. The peak hardness and peak strength of the CR alloy are increased because of quantity increasing and refinement of S′ phase and high density dislocation.

Influence of pre-deformation on age-hardening response and mechanical properties of extruded Mg-6%Zn-1%Mn alloy

The effect of cold plastic deformation between solution treatment and artificial aging on the age-hardening response and mechanical properties of alloy was investigated by micro-hardness test,tensile test,optical microscopy（OM） and TEM observation.After solution treatment at 420 ℃ for 1 h,three kinds of pre-deformation strains,i.e.0,5% and 10%,were applied to extruded ZM61 bars.Age-hardening curves show that pre-deformation can significantly accelerate the precipitation kinetics and increase peak-hardness value;however,as pre-deformation strain rises from 5% to 10%,there is no gain in peak hardness value.The room temperature（RT） tensile properties demonstrate that increasing the pre-deformation degree can enhance the yield strength（YS） and ultimate tensile strength（UTS） but moderately reduce elongation（EL）;furthermore,the enhancement of YS is larger than that of UTS.No twin can be observed in 5% pre-deformed microstructure;however,a large number of twins are activated after 10% pre-deformation.The peak-aged TEM microstructure shows that pre-deformation can increase the number density of rod-shaped β 1 ＇ precipitates which play a key role in strengthening ZM61 alloy.

Effects of high temperature pre-straining on natural aging and bake hardening response of Al-Mg-Si alloys

The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.

Influence of pre-strain and heat treatment on subsequent deformation behavior of extruded AZ31 Mg alloy

Pre-compression and heat treatment were performed on an extruded AZ31 Mg alloy,and their effects on subsequent deformation behavior were investigated.The results show that at low temperature annealing(170 ℃ for 4 h),the extruded samples with and without annealing exhibit a nearly equivalent yield stress(~148 MPa) because their microstructures are nearly unchanged.However,under the same annealing condition,the yield stress of sample with pre-twinning and subsequent annealing(~225 MPa) is higher than that of the pre-twinned one(~200 MPa).The former sample presents a hardening effect because the solute atoms segregated on twin boundaries lead to a strengthening effect.The pre-twinned sample annealed at 400 ℃ for 1 h shows a higher ultimate elongation(~28%) than the pre-twinned one(~15%),but its yield stress(~125 MPa) is much lower than that of the pre-twinned one(~200 MPa).