Effect of homogenization heat treatment on the microstructure and heat- affected zone microfissuring in welded cast alloy 718

The effect of homogenization temperature on microfissuring in the heat-affected zones of electronwelded cast INCONEL 718 has been studied. The material was homogenized at various temperatures in the range of 1037 ° to 1163 ° and air-cooled. The homogenized material was then electron-beam welded by the bead-on-plate welding technique. The microstructures and microfissuring in the heat-affected zone (HAZ) were evaluated by analytical scanning electron microscopy (SEM). The grain boundary segregation of various elements was evaluated by secondary ion mass spectroscopy (SIMS). It was observed that the total crack length (TCL) of microfissures first decreases with homogenization temperature and then increases, with a minimum occurring in the specimen heat treated at 1163 °. This trend coincides with the variation in segregation of B at grain boundaries with homogenization temperature and has been explained by equilibrium and nonequilibrium segregation of B to grain boundaries during the homogenization heat treatment. No other element was observed to segregate at the grain boundaries. The variation in volume fraction of phases like δ-Ni₃Nb, MC carbide, and Laves phases does not follow the same trend as that observed for TCL and B segregation at the grain boundaries. Therefore, microfissuring in HAZ of welded cast INCONEL 718 is attributed to the segregation of B at the grain boundaries.     

Effect of intermediate annealing on texture evolution and plastic anisotropy in an Al-Mg autobody alloy

The effect of intermediate annealing (IA) on texture evolution and plastic anisotropy of an Al-Mg autobody sheet was investigated. The formation of annealing textures after two kinds of final heat treatments was discussed with the aid of microstructural characterization. The results showed that the IA treatment had obvious influences on the final annealing texture as well as the resulting plastic anisotropy. It led to relatively lower recrystallization extent and stronger retained rolling orientations in the sheets after final heat treatment. The final annealing textures were very weak due to the dominant influence of particle stimulated nucleation. The other orientations occurring can either be attributed to genuine recrystallization or to recrystallization in situ. As a result of good suppression of the cube and rotated cube orientations, a good combination of normal anisotropy and planar anisotropy was achieved in the sample with IA and after O treatment.     

热处理工艺对Cu-Ni-Si合金组织与性能的影响

采用3种不同的工艺(直接在450℃下进行时效处理;80%冷轧,然后在450℃下进行时效处理;600℃/8 h高温预时效+80%冷轧+780℃/2 min+450℃/16 h终时效)对固溶处理后的Cu-2.0Ni-0.34Si-Mg合金进行形变热处理,研究形变热处理工艺对该合金的组织与硬度及电导率的影响。结果表明:采用第3种工艺对合金进行形变热处理,由于其中的短时高温预处理可以获得溶质原子充分固溶的过饱和固溶体,因此终时效后的合金具有最佳的综合性能,显微硬度为180 HV,相对电导率为49.8%IACS,伸长率为13%。合金的平均晶粒尺寸约为20μm,主要析出强化相为δ-Ni2Si。     

热处理对FGH95合金组织和性能的影响研究

通过热处理工艺试验设计,研究了不同热处理条件下FGH95合金的组织和性能。与亚固溶线温度热处理后细晶试样比较,过固溶线温度热处理的试样获得了晶粒度8级的相对粗晶组织,强度仅比细晶试样的降低不超过5%,而蠕变性能显著提高,700℃/690MPa条件下,0.2%残余应变的蠕变寿命提高了3～4倍;另外,通过优化γ’相的尺寸与分布,可进一步提高合金的力学性能。     

热处理对GH1016合金组织和性能的影响

为解决GH1016合金在600~800℃温度区间的中温低塑性问题,本文提出一种新的热处理制度.采用1 160℃×30 min炉冷到950℃×120 min,然后空冷的热处理制度,在20~950℃的条件下对处理后的合金试样进行拉伸性能测试并对拉伸断口进行分析.结果表明,经过改进的热处理制度处理后,合金的晶界析出大量的碳化物,阻止了拉伸时裂纹的萌生和扩展,从而提高了合金的塑性.     

热处理制度对汽车用TC6钛合金组织及性能的影响

采用四种不同热处理制度对汽车用TC6钛合金棒材进行了等温退火试验,并进行了试样显微组织、耐磨损性能和耐腐蚀性能测试与分析.结果 表明,采用"870℃保温1.5 h,炉冷至600℃保温2h,空冷"热处理制度(1#试样)时,合金的耐磨损和耐腐蚀性能最差;采用"900℃保温1.5h,炉冷至600℃保温2h,空冷"热处理制度(...     

热处理和锰含量对CuZnAl合金微观组织结构和宏观性能的影响

采用万能试验机、金相显微镜、扫描电子显微镜以及动态热机械分析仪,研究了时效时间以及Mn元素对CuZnAl合金微观组织结构、力学及阻尼性能的影响。结果表明:Mn元素可以改善材料微观组织结构,提高合金的阻尼性能和拉伸强度;微观组织结构中的针状马氏体和块状马氏体随时效热处理时间的增长发生显著变化,并由此影响材料的阻尼性能;阻尼性能与针状马氏体的长度和密度呈正相关,而与块状马氏体的数量呈负相关,但Mn含量过高时,例如达到10%,出现粗大的块状组织,合金力学性能会有明显下降。     

热处理工艺对近α钛合金组织与性能的影响

研究了固溶和时效工艺参数对一种近α钛合金Ti-5Al-2Nb-2Zr-1.5Mo显微组织与力学性能的影响.结果表明:在α+β两相区,随着固溶温度的升高,初生α相含量(体积分数,下同)减少,亚稳相含量增加,冷却过程中分解的针状马氏体α'相使合金的硬度升高;时效温度的变化通过影响α'相分解析出次生α相的尺寸、数量及分布方式...     

Effect of the size distribution of alpha particles on microstructure evolution during heat treatment of an alpha/beta titanium alloy

A model was developed to describe the diffusional growth of a size distribution of alpha particles in Ti-6Al-4V during cooldown following alpha/beta solution treatment. Model results for initial microstructures with the same initial volume fraction of alpha but comprising either a distribution of particle sizes or a uniform particle size (equal to the average size of the distribution) yielded almost identical results in terms of final volume fraction and average particle size. The simulations quantified the narrowing of the size distribution associated with the different growth rates of small and large particles.     

退火工艺对Ti-IF钢合金化热镀锌板微观组织织构的影响

研究了再结晶退火温度、退火时间对Ti-IF钢合金化热镀锌板的钢基组织织构及析出相的影响.研究结果表明:在生产中控制退火温度>800 ℃,退火时间≥60 s,维持机速约60 m/min,可获得具有完全再结晶钢基组织、有利织构和较多析出相的产品.此钢板具有优良的成型性能,能够满足用户的要求.     

第二组元对铁基高温合金显微组织的影响

采用气体雾化法制备Fe-12Cr-2.5W-0.4Ti-0.25(Y2O3)铁基合金粉末,分别在该粉末中添加1%Al粉和1%Fe2O3粉,在1 250℃下热挤压,随后在1 050℃热处理。通过X射线衍射、扫描电镜和光学显微镜等研究Al和Fe2O3对铁基合金热挤压和热处理态显微组织的影响。结果表明:与基体合金相比,Al的添加可促进铁素体基体中元素的扩散,导致晶粒尺寸增大,同时由于Fe、Al互扩散系数的差异引起柯肯达尔效应,使合金孔隙度增大;添加Fe2O3后合金的孔隙度更大,氧化物和大量残余孔隙阻碍晶粒长大,因而晶粒尺寸减小。3种合金在1 050℃进行热处理时晶粒的长大规律均满足BECK方程,添加Al可提高合金的晶粒生长指数,而添加Fe2O3则相反。     

Effect of heat treatment conditions on the structure and mechanical properties of a cast Al-Li-Cu aluminum alloy

Quenching and one- and two-stage aging conditions are found for a high-strength Al-Li-Cu cast alloy with a low density from the results of studying its structure, mechanical properties, and aging kinetics.     

热处理对GH3128合金接头组织及力学性能的影响

 核能已经逐渐取代化石能源成为新一代能源,作为重要构件的高温气冷堆中间换热器得到了广泛关注。由于GH3128合金具有较好的焊接性、较高的高温抗氧化性能和组织稳定性,有望成为超高温气冷堆中间换热器的候选材料,但基于换热器结构复杂性以及密封性的要求,焊接是其生产和制造的关键成形手段。采用脉冲钨极氩弧焊(GTAW)对GH3128合金2 mm板材进行对接焊,研究了热处理对焊接焊接接头显微组织以及应力的影响。结果表明,在优化焊接工艺参数下,固溶态板材接头表现出最高的强塑性,室温及高温拉伸断裂位置均为母材。由于热轧态与固溶态板材接头热影响区在焊接过程中产生残余应力,导致该区硬化,在高温变形过程中残余应力诱发热影响区μ相析出,对接头持久、蠕变性能造成不利影响。焊后热处理消除了接头热影响区的残余应力,减少了持久、蠕变过程中μ相的析出,接头持久寿命得以改善。在1 200 ℃下,残余应力可为焊后热处理过程中静态再结晶提供激活能,接头热影响区发生再结晶,硬度下降,接头塑性变形能力不协调,导致室温拉伸与950 ℃拉伸断裂位置均为焊接接头。对固溶态板材试样进行不同的焊后热处理,EBSD扫描结果分析发现,接头经过1 100 ℃×10 min热处理后,残余应力明显消失,温度升高至1 140 ℃后,热影响区开始发生再结晶。     

热处理工艺对热挤压变形粉末高温合金FGH95组织与性能的影响

对比研究了FGH95合金在不同热加工工艺和热处理制度下合金的组织及γ'的分布,用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)观察了不同热处理制度处理后合金的组织及时效后γ'的中心暗场相,测试了室温(20℃)和高温(650℃)材料的拉伸性能,并对高温瞬时断裂区断口进行了对比分析.结果表明:相同热处理工艺,HIP温度越高,时效析出的γ'相尺寸越大;不同热处理制度均能够改变γ'的分布;盐浴冷却明显增大中等尺寸γ'相数量,显著提高合金高温塑性.     

The effect of predeformation and heat treatment on microstructure of Al-7.0% Si-0.45% Mg alloy cast through SIMA route

The effect of warm working, hot working and heat treatment conditions on microstructure of Al-7.0%Si-0.45%Mg alloys were investigated in strain induced melt activation (SIMA) process. Predeformation of 30%, 40% and 50% was done by hot working. The hot working has been carried out at 380°C. The samples of various deformations were kept at 580°C, 590°C, 600°C with varied soaking time for 10, 20, 30 min respectively. It was found that increased predeformation reduced the soaking time to obtain globular α Al grains. The shape factor and metallography were done on SIMA processed Al-7.0%Si-0.45%Mg alloys. Those were compared with as cast Al-7.0%Si-0.45%Mg alloy and it was observed that strain induced predeformation and subsequently melt activation has caused the globular microstructure of the alloy.     

Mechanical properties and microstructure of centrifugally cast alloy 718

The relationship between the microstructure and mechanical properties of alloy 718 was investigated for two discs centrifugally cast at 50 and 200 rpm and given a duplex age heat treatment. The results of mechanical property tests at temperatures from 426 to 649 °C showed that the tensile yield and ultimate strength levels of both castings were similar. However, the creep-rupture properties were considerably enhanced for the casting produced at 200 rpm. Comparison of the radial and transverse creep properties of each disc indicated that creep life was generally independent of orientation, but ductility was greatest for specimens oriented transverse to the radial direction of the casting. Fatigue crack propagation performance was not greatly influenced by orientation or mold speed parameters and was comparable to wrought alloy 718 when compared on the basis of stress intensity factor range. The centrifugal casting process was found to produce a homogeneous microstructure free of porosity but with the expected segregation of solute alloying elements to Laves and carbide phases. The effect of the as-cast microstructure on the mechanical behavior and the potential influence of hot isostatic pressing to improve the microstructure are discussed.     

双相区热处理对430铁素体不锈钢热轧板组织和性能的影响

研究了α+γ双相区热处理对430铁素体不锈钢热轧板显微组织和力学性能的影响,并与工业罩式炉退火后的热轧板显微组织和力学性能进行了对比分析。结果表明:在双相温度区间对430不锈钢热轧板进行热处理,分割了热轧板轧向的条带状组织,抑制了聚集组织的形成。与常规罩式炉退火工艺相比,双相区热处理显著提高了430不锈钢热轧板的伸长率,降低了屈服强度和硬度,有利于改善最终冷轧产品的冲压性能和抗起皱性。     

Sn和冷轧板厚度对取向硅钢初次再结晶组织和织构影响

研究了Sn含量和冷轧板厚度对取向硅钢冷轧板脱碳渗氮退火后组织和织构的影响,发现随着厚度减小和Sn含量增加,初次再结晶晶粒尺寸趋于减小,增加Sn含量导致对Goss取向形成的不利织构{001}〈120〉增加,而钢板厚度减薄时{111}〈112〉、{411}〈148〉等有利织构和{001}〈120〉不利织构均增加。Sn在氧化层中的含量显著小于基体,在氧化层/基体的界面处有显著的浓度梯度。虽普遍认为Sn的晶界偏聚是影响退火组织和织构的原因,但俄歇电子能谱只能偶然检测到,推测或是该偏聚不具有普遍性,或是其偏聚厚度极小超出了仪器检测的范围。     

Structural evolution of a strip-cast al alloy sheet processed by continuous equal-channel angular pressing

Experiments were conducted on strip-cast 1050 Al alloy sheets using an equal-channel angular pressing (ECAP) process to investigate the feasibility of the technique for producing metal strips. The developed process is capable of introducing shear deformation into metal strips in a continuous mode at a relatively fast forming speed of 10 to 50 m/min. The actual shear-flow patterns as a result of the continuous ECAP were demonstrated and compared with those obtained from numerical calculations. The effects of die geometry on the mechanical properties of the strips were investigated. Observations of the microstructural evolution in the equal-channel angular pressed (ECAPed) samples were conducted using transmission electron microscopy (TEM) as a function of oblique angles. The texture evolution was investigated using orientation distribution function (ODF) analysis. A possible application of this process for producing an Al alloy sheet with high formability and low earing was discussed by calculating the Lankford parameter and the planar anisotropy.     

Effect of thermomechanical treatment on the evolution of rolling and recrystallization textures in twin-belt cast AA5754 aluminum alloy

The relative importance of shear banding, particles, and grain size in determining the rolling and recrystallization textures of a twin-belt strip cast AA5754 aluminum alloy has been investigated. Various thermomechanical processing schedules have been employed that incorporate homogenization, warm and cold rolling, and intermediate anneals in various combinations prior to a final recrystallization treatment. Despite its inherent susceptibility, the alloy undergoes limited shear banding during rolling and displays a large random component of the deformation texture. The effect is most pronounced in the as-cast alloy subjected to cold rolling without any prior or intermediate heat treatments. This can be attributed to the denser distribution of particles, a greater scattering of the initial texture, and a relatively small grain size. Homogenizing prior to cold rolling promotes more extensive shear banding and accelerates the development of a strong rolling texture. A grain shape effect results in a prominent S component in the rolling texture at higher reductions, irrespective of the processing history of the material. In the heavily rolled as-cast alloy, the recrystallization texture is dominated by Cube and R components indicating the prevalence of oriented growth processes. However, homogenizing the as-cast alloy prior to cold rolling imparts a characteristic recrystallization texture with strong CH component, which is most likely due to selected growth of grains following particle-stimulated nucleation.