Property and microstructure analysis of ZK60 alloy superplastic sheet

It was investigated that the superplastic mechanical properties of fine-grained ZK60 magnesium alloy sheets at the temperature range of 200-420 ℃ and strain rate range of 5.56 × 10-4 -5.56 ×10-2 s-1 by tensile tests.And the microstructure evolution during the superplastic deformation of ZK60 magnesium alloy was examined by metallurgical microscope and transmission electronic microscope (TEM).The results showed that fine-grained ZK60 magnesium alloy starts to exhibit superplasticity from 250 ℃ and the maximum elongation is about 1106% at 400 ℃ and 5.56 × 10-4 s-1.The strain rate sensitivity is significantly enhanced with the increase of temperature and with the decrease of strain rate.The predominate superplastic mechanism of ZK60 magnesium alloy is grain boundary slide (GBS) at the temperature range of 300-400 ℃.The grains of ZK60 alloy remain equaxial after superplastic deformation,and dynamic continuous recrystallization (DCRX) is an important softening mechanism and grain stability mechanism during the superplastic deformation of the alloy.The curved grain boundaries and crumpled bands at grain boundaries after deformation prove GBS generates during superplastic deformation of ZK60 magnesium alloy.     

Inconel718合金多层夹芯筒结构LBW/SPF技术研究

研究了超细晶Inconel718合金激光对接板高温塑性及多层夹芯筒结构的LBW/SPF成形技术。结果表明:垂直焊缝拉伸时最大延伸率发生在温度为950℃、应变速率为3.1×10-4s-1条件下,为400.6%,平行焊缝拉伸时最大延伸率发生在温度为965℃,应变速率为6.2×10-4s-1条件下,为164.0%。对接板在950～980℃相对胀形高度均高于1.0。通过设计直径可变的卡具以及采取点焊加固等措施,解决了多层夹芯结构的激光焊接难题。激光穿透焊参数:功率1 200 W,焊速1 200 mm/min,离焦量-1 mm,保护气体流量0.6 L/min,超塑成形参数:温度Tf=965℃,压力Pf=4.2 MPa,时间tf=130 min。采用LBW/SPF技术制造的多层夹心筒结构具有外观形状好、壁厚分布均匀、内部结构对称度高等优点。     

超硬铝合金LC9的超塑性效应

本文采用了简单的预处理工艺,开发超硬铝合金LC9的超塑性;并以等温拉伸试验和等温压缩试验相互对照、相互补充的试验方法,考察LC9的超塑性唯象学特性。结果表明,该合金的最高延伸率可达220％,m值为0.4,流动应力最低可达10MPa;最佳超塑性变形条件为:温度420℃,应变速率1.67×10~(-3)s~(-1)。     

1420铝锂合金超塑性行为

以1420铝锂合金作为实验材料,通过改变应变速率来探求最佳的超塑性变形条件,即延伸率大幅度提高和获得变形均匀的细小微观组织。研究发现当温度为480℃,应变速率为3×10-4s-1时可以获得最佳超塑性变形状态,此时延伸率δ=550％,流变应力σ=1.9MPa。同时通过金相分析以及TEM微观组织观察发现,在此条件下的组织等轴性好同时晶粒分布细小均匀,出现了细小的再结晶亚晶粒,有助于超塑性变形的进行。     

Hot deformation behaviors and flow stress model of GCr15 bearing steel

The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950℃ and 1150℃ and strain rates between 0.1 and 10 s^-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150℃ and strain rate range of 0.1-10 s^-1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization （DRX） grain size were also established. The model predictions show good agreement with experimental results.     

间断变形工艺提高AZ31镁合金超塑性的研究

研究间断变形工艺对AZ31镁合金超塑性的影响。结果表明,当温度为400-440℃、应变速率小于5×10^-4s^-1时,间断变形工艺可以显著提高AZ31镁合金的超塑性。计算了空洞体积分数与空洞数量的关系。结果表明,空洞体积分数与空洞数量呈正比。对拉伸试样断口形貌的分析表明,间断变形减少了空洞数量,因而减小了空洞体积分数,提高了超塑性伸长率。     

中温压力容器钢12CrMo的高温塑性研究

通过热模拟试验对中温压力容器钢12CrMo连铸坯的高温塑性进行研究。在不同的变形温度下采用10-3s-1的应变速率对试样进行拉伸变形,测量拉伸断口的面缩率,并对拉伸断口的显微组织和析出物进行分析。结果表明,当变形温度高于900℃时,试样在拉伸过程中发生动态再结晶,其面缩率大于85%,表现出优良的高温塑性;当变形温度为850℃时,有大量细小的AlN在12CrMo钢中弥散析出,其尺寸约为10 nm;当变形温度降至800℃时,大量的先共析铁素体沿奥氏体晶界析出,形成网状结构,试样面缩率降至36%,12CrMo钢的高温塑性显著下降。     

稀土对4145H钻铤钢动态再结晶的影响

应用Geeble-1500D热模拟试验机分别对稀土含量为6×10-6和16×10-6的钻铤钢进行单道次压缩实验,测定其不同终轧温度下的真应力-真应变曲线,采用应变速率0.01 s-1,变形量60%,终轧温度为850,950,1050,1150℃,研究不同稀土含量,不同终轧温度对钻铤钢再结晶的影响。结果表明,稀土含量为16的钻铤钢能显著地抑制形变奥氏体的动态再结晶。     

Dynamic mechanical behavior and microstructural evolution of the Al-6Mg alloy subjected to three treatment conditions

The mechanical properties of Al-6Mg alloy with three treatment states (H112, O and cold-extruded states) were investigated at room and high temperatures using an INSTRON machine and a Split Hopkinson Pressure Bar (SHPB). Stress-strain curves of the alloy with different processes were obtained at a quasi-static strain rate of 5×10-4 s-1and dynamic strain rates of 1 400-4 200 s-1, respectively. The results suggest that, at room temperature, the three processed Al-6Mg alloys are all low sensitive to strain rate. The O state Al-6Mg alloy (Al-6Mg-O) exhibits the most ductility, while the cold-extruded Al-6Mg alloy (Al-6Mg-C) displays the highest strength. At elevated temperatures, the yield stresses and the differences in yield stress of the three processed alloys all decrease with increasing temperature under the quasi-static strain rate of 5×10-4 s-1. Based on test results, modified Johnson-Cook (JC) constitutive models for the three processed Al-6Mg alloys were developed. The microstructures before and after deformation were examined by electron backscattered diffraction (EBSD) and further dynamic recrystallization (DRX) at the strain rate of 3 300 s-1 was discussed.     

Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10-4 to 10-2 s-1 by uniaxial tensile tests. An excellent superplasticity with the maximum elongation to failure of 1020% was obtained at 753 K and the strain rate of 1.04×10-3 s-1 and its strain rate sensitivity, m, is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition, micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy. Grain boundary sliding (GBS) was considered to be the main deformation mechanism during the superplastic deformation. Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in super-plastic deformation.     

Flow stress behavior of Al-Cu-Li-Zr alloy containing Sc during hot compression deformation

The flow stress behavior of Al-3.5Cu-1.5Li-0.25（Sc＋Zr） alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s^-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa^-1 and 1.51×10^16 s^-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.     

Superplastic behavior of reciprocating extruded Mg-6Zn-1Y-0.6Ce-0.6Zr from rapidly solidified ribbons

RRE-Mg66 alloy with a composition of Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6Zr was prepared by combinatorial processes of rapid solidification, reciprocating extrusion and extrusion. Microstructure was evaluated on SEM and TEM. The average grain size of the alloy is 0.7 ??m, the size of the second phase at grain boundary is 0.15 ??m, and the size of the intragranular precipitates in round shape is less than 20 nm. Superplastic behavior of the material was investigated in a temperature range of 150 to 250 °C and initial strain rate range of 3.3×10^?4 to 3.3×10^?2 s^?1 in air. The highest elongation of 270% was obtained at 250 °C and 3.3× 10^?3 s^?1. High-strain-rate superplasticity and low-temperature superplasticity were achieved. The superplasticity results from intragranular sliding (IGS) at temperatures from 170 to < 200 °C and grain boundaries sliding (GBS) at 250 °C. At 200 °C a combination of IGS and GBS contributes to the superplastic flow.     

Hot deformation behavior of FGH96 superalloys

1. Introduction Precipitation-hardened nickel-based superalloys have been widely used as high-temperature structural materials in gas turbine engine applications for more than 50 years. Because powder metallurgy (P/M) process produces a fine, homogenous a…     

含稀土的23Cr型双相不锈钢的高温变形行为

利用Gleeble-3500热力模拟试验机在950-1200℃,应变速率为0.1-10s-1条件下进行了含稀土的23Cr型双相不锈钢的热压缩变形,获得了流变曲线,建立了热变形方程,分析了变形组织。结果表明：在流变曲线上既存在峰值应力也有稳态应力;在高温低应变速率条件下,峰值应变减小。上述变形条件下,试验钢的热变形激活能Q=436kJ/mol,表观应力指数n=3.91,热变形方程为：ε=2.41×1016[sinh（0.012σs）]3.91exp （-436000/RT）。奥氏体的动态再结晶在试验钢的动态软化机制中起主导作用且随着温度的升高和应变速率的降低越来越充分;而大应变下,铁素体的软化主要表现为较充分的动态回复。稀土元素影响了热变形时两相中Mo元素的再分配是稀土改善双相不锈钢高温塑性的重要原因之一。稀土使Mo在铁素体中浓度较低温度下降低,高温下升高;而奥氏体相中,使得Mo浓度在较低温度下升高而高温下降低。     

Study on the isothermal oxidation behavior in air of Ti_3AlC_2 sintered by hot pressing

The isothermal oxidation behavior at 900―1300℃ for 20 h in air of bulk Ti3AlC2 with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10-10 kg2·m-4·s-1 at 900℃ to 5.56×10-9 kg2·m-4·s-1 at 1300℃. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti3AlC2 had excellent oxidation resistance due to the continuous, dense and adhesive protect scales consisted of a mass of α-Al2O3 and a little of TiO2 and/or Al2TiO5. In principle, the oxide scale was grown by the inward diffusion of O2- and the outward diffusion of Ti4 and Al3 . The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps, and holes.     

GH4169合金δ相的析出动力学研究

采用X射线衍射技术测定了GH4169合金中δ相在900℃、930℃时的析出动力学,并采用光学显微镜进行组织观察,结果表明：δ相的形核位置和形核方式与时效温度有关.当时效温度在900℃时,δ相主要在晶界和孪晶界上形核析出,而晶内颗粒状δ相由时效初期析出的亚稳态γ″相转变形成;当时效温度为930℃时,δ相不仅可以在晶界和孪晶界形核析出,还可以从基体γ莫直接形核析出,并且随着时效时间的延长,δ相逐渐向晶内生长,最终形成魏氏体δ相.当时效温度一定时,δ相的析出含量与时效时间满足Avram i方程.     

Superplasticity and superplastic bulging behavior of ZrO<Subscript>2</Subscript>/Ni nanocomposite

ZrO2/Ni nanocomposite was produced by pulse electrodeposition and its superplastic properties were investigated by the tensile and bulging tests. The as-deposited nickel matrix has a narrow grain size distribution with a mean grain size of 45 nm. A maximum elongation of 605% was observed at 723 K and a strain rate of 1.67×10-3s-1 by tensile test. Superplastic bulging tests were subsequently performed using dies with diameters of 1 mm and 5 mm respectively based on the optimal superplastic forming temperature. The effects of forming temperature and gas pressure on bulging process were experimentally investigated. The results indicated that ZrO2/Ni nanocomposite samples can be readily bulged at 723 K with H/d value (defined as dome apex height over the die diameter) larger than 0.5, indicating that the nanocomposite has good bulging ability. SEM and TEM were used to examine the microstructure of the as-deposited and bulged samples. The observations showed that significant grain coarsening occurs during superplastic bulging, and the microstructure is found to depend on the forming temperature.     

Influence of isothermal aging onσprecipitation in super duplex stainless steel

The time-temperature-transformation (TTT) curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastot-digital thermal dilatometer,and the influence of isothermal aging on σ precipitation was studied by metallographic observation,X-ray diffraction (XRD),and transmission electron microscopy (TEM).The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000℃,especially in the range of 800-900℃.The longer the aging time,the higher the amount of σ precipitation.The area fraction of various phases remains at a certain value upon the completion of ferrite deformation.The temperature of 850℃ is the most sensitive transaction temperature,the incubation time for the formation of o precipitation is less than 1 min,and aging for 20 min leads to the complete transformation of ferrite.The o phase is formed preferentially at the α/α/γ junction,and then grows along the α/α boundary in the matrix.     

Plastic deformation behavior of ZK60 magnesium alloy with addition of neodymium

The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.     

CN—18催化剂上甲烷蒸汽转化宏观动力学研究

CN－18气态烃蒸汽转化催化剂是以α－Al