Anisotropy in Mechanical Properties and Fracture Behavior of an Oxide Dispersion Fe20Cr5Al Alloy

Anisotropy of fracture toughness and fracture behavior of Fe20Cr5Al oxide dispersion-strengthened alloy has been investigated by means of compression tests, hardness tests, and wedge splitting test. The results show a small effect of the compression direction on yield strength (YS) and strain hardening. The YS is minimum for longitudinal direction and maximum for the tangential direction. The transverse plastic strain ratio is similar for tangential and longitudinal directions but very different from that in normal direction. Hardness depends on the indentation plane; it is lower for any plane parallel to the L-T plane and of similar magnitude for the other orthogonal planes, i.e., the L-S and T-S planes. Macroscopically, two failure modes have been observed after wedge-splitting tests, those of LS and TS specimens in which fracture deviates along one or two branches normal to the notch plane, and those of LT, TL, SL, and ST specimens in which fracture propagates along the notch plane. Besides LT and TL specimens present delaminations parallel to L-T plane. Both, the fracture surface of branching cracks and that of the delaminations, show an intergranular brittle fracture appearance. It is proposed that the main cause of the delamination and crack branching is the alignment in the mesoscopic scale of the ultrafine grains structure which is enhanced by the 〈110〉-texture of the material and by the presence in the grain boundaries of both yttria dispersoids and impurity contaminations. An elastoplastic finite element analysis was performed to study what stress state is the cause of the branches and delaminations. It is concluded that the normal to the crack branches and/or the shear stress components could determine the crack bifurcation mechanism, whereas the delamination it seems that it is controlled by the magnitude of the stress component normal to the delamination plane.     

Microstructures and Mechanical Properties of Al89Gd7Ni3Fe Alloy Extruded from Its Amorphous Powders

The microstructures and mechanical properties of Als9 GdTNi3Fe alloy extruded from its amorphous powder were investigated at different temperatures. Devitrification process of amorphous phase was also analyzed. As a result, the microstructure of the extruded alloy consists of fee α-Al, binary intermetallic Al3Gd and ternary intermetallic r l phase. The grain size of α-Al is fine. The intermetallic Al3Gd exists as equiaxed particle and τ1 phase appears rod like.     

ZTA15Cr铸造钛合金材料的组织及性能

研究了ZTA15Cr铸造钛合金材料在铸造状态和热等静压状态下的力学性能和微观组织。结果表明,ZTA15Cr铸造钛合金在铸造状态下组织以马氏体＋晶界α＋针状α为主,强度高而塑性较差,力学性能数据分布离散性强,不能满足使用要求;经热等静压处理后,组织中的板条状α＋β交叉呈网篮状,塑性有较大提高,可满足航空航天对钛合金铸件的使用要求。     

热压加工对含铬、镍块体纳米晶Fe3Al组织和性能的影响研究

对通过铝热反应熔化制备的含10%(质量分数,下同)的铬和10%镍的块体纳米晶Fe3Al材料在不同温度、不同次数下进行了热压加工。利用XRD研究了热压加工前后纳米晶粒尺寸的变化,并测试了硬度变化和压缩率。结果显示:含10%铬的纳米晶Fe3Al在600℃表现出较好的塑性变形能力,材料在热压加工前后都是由无序bcc结构的Fe3Al相组成;含10%镍的纳米晶Fe3Al在800和1 000℃表现出较好的塑性变形能力,材料在热压加工前为无序bcc结构的Fe3Al相,在1 000℃热加工后,已转变为DO3有序结构;两种材料的压缩率都随着热压加工次数的增加逐渐增大。含10%铬的纳米晶Fe3Al在600℃和含10%镍的纳米晶Fe3Al在1 000℃随着热压加工次数的增加,晶粒尺寸都发生了增大,但材料硬度变化不大。     

耐热合金Cr25Ni30组织性能研究

研究设计了三种不同成分Cr25Ni30耐热合金,并对其组织特征及常温和高温性能进行了测定。结果表明:w(Al)为5%的合金室温拉伸强度最高,金属组织中出现较多的Ni-Al金属间化合物,显著降低其塑性;w(Al)为3%的合金塑性最好,但强度较低;w(Nb)为2%的合金抗氧化性最好,高温强度最高,综合性能最好。     

Al1.5Co4Fe2CrCux高熵合金的电磁吸波性能

高熵合金由于其在恶劣环境中的适用性以及对电磁场的多种衰减机制,使其在吸波领域具有巨大的潜在优势和广阔的应用前景。因Cu元素具有优异的延展性和导电性而被广泛应用,添加Cu元素以探究不同Cu含量下Al_1.5Co₄Fe₂CrCu_x (x=0.5, 1.0, 1.5, 2.0;摩尔比)高熵合金的吸波性能。结果表明,通过机械合金化制备的Al_1.5Co₄Fe₂CrCu_x高熵合金为片状、粒状和椭球状,具有软磁特性;饱和磁化强度随着Cu含量的增大逐渐减小,矫顽力则逐渐增大;同时,添加Cu元素有助于形成大长径比的粉末颗粒,调节合金粉末的磁性能和电磁性能,进一步增强合金粉末的介电损耗能力。当x=1.0时,Al_1.5Co₄Fe₂CrCu高熵合金粉末具有最高的衰减系数,在1.50 mm的较薄厚度下其最小反射损耗为-16.50 dB, 1.70 mm厚度下其在Ku波段的有效...     

Microstructural Evolution and Mechanical Response of Equal-Channel Angular Extrusion-Processed Al-40Zn-2Cu Alloy

Microstructural evolution, tensile properties, and impact toughness of an aluminum-zinc-copper (Al-40Zn-2Cu) alloy subjected to repetitive equal-channel angular extrusion (ECAE) up to four passes following either route A or route B_C were investigated. The experimental results reveal that the ECAE eliminated as-cast dendritic microstructure along with casting defects such as microporosities almost completely. The ECAE-processed samples consisted of mostly elongated microconstituents via route A and equiaxed microconstituents via route B_C. The high stresses imposed in ECAE lead to the fragmentation of the copper-rich θ phase into smaller particles with significant fragmentation occurring in the first pass and additional breaking in the subsequent passes in both routes. The ECAE processing simultaneously increased both the strength and ductility of the alloy as compared to the as-cast state, regardless of the processing route and number of passes. The deformation behavior of as-cast Al-40Zn-2Cu alloy has changed from brittle to ductile mode after ECAE due to the microstructural refinement, deformation-induced homogenization, and reduction of porosities. The limited impact toughness of as-cast alloy was significantly improved by multipass ECAE, especially in route A.     

微量硼和铌对铸造Ni50Al20Fe30合金组织及性能的影响

研究了微量硼和2％Nb对铸造Ni50Al20Fe30合金组织及性能的影响。结果表明：微量硼的加入可以改善Ni50Al20Fe30合金的强度与塑性,最佳硼含量为0．02％－0．05％;此外,微量硼的加入影响该合金的共晶区,从而明显改变合金的微观组织形态。在硼含量为0．02％时,该合金主要处于β相（NiAl)与γ相的共晶区,这对合金的室温塑性极为有利。添加2％Nb可明显提高合金的压缩屈服强度并改善塑性。在室温、650℃和10000170,该合金的压缩屈服强度分别提高30％,59％和36％。     

Microstructural Evolution and Mechanical Properties of Short-Term Thermally Exposed 9/12Cr Heat-Resistant Steels

The microstructural evolution during short-term (up to 3000?hours) thermal exposure of three 9/12Cr heat-resistant steels was studied, as well as the mechanical properties after exposure. The tempered martensitic lath structure, as well as the precipitation of carbide and MX type carbonitrides in the steel matrix, was stable after 3000?hours of exposure at 873?K (600?°C). A microstructure observation showed that during the short-term thermal exposure process, the change of mechanical properties was caused mainly by the formation and growth of Laves-phase precipitates in the steels. On thermal exposure, with an increase of cobalt and tungsten contents, cobalt could promote the segregation of tungsten along the martensite lath to form Laves phase, and a large size and high density of Laves-phase precipitates along the grain boundaries could lead to the brittle intergranular fracture of the steels.     

Thermally Induced Microstructural Transformations of Fe72Si15B8V4Cu1 Alloy

Thermal stability, mechanism, and kinetics of thermally induced microstructural transformations and their effects on magnetic permeability of Fe₇₂Si₁₅B₈V₄Cu₁ alloy with combined amorphous/nanocrystalline structure were studied. DTA curves revealed two separated thermally activated exothermic events in the temperature ranges from 740 K to 820 K (467 °C to 547 °C) and 870 K to 930 K (597 °C to 657 °C). Crystalline phases present in the as-prepared and thermally treated alloy samples were identified, and their microstructural parameters were determined using XRD, while, to gain further insight into the mechanism of microstructural transformations, AFM and SEM–EDS analyses were performed. Deconvolution of the complex DTA peak into individual steps was conducted, and, in correlation with the results of microstructural analysis, kinetic triplets corresponding to individual transformation steps were determined, allowing for the estimation of the lifetimes of the alloy at different temperatures. Magnetic permeability measurements showed that, in spite of the influence of microstructural transformations on magnetic properties of the alloy, the favorable magnetic properties are retained over relatively a wide temperature range.

     

Fe 15C 15Cr 15Al超高碳钢碳化物的球化和力学性能

 对Fe 15C 15Cr 15Al超高碳钢碳化物的球化工艺及力学性能进行了研究。扫描电镜观察表明，加入铝，可抑制锻后空冷条件下先共析网状碳化物的析出；利用铝合金化作用和成分不均匀化奥氏体加热控制，提出了2种无形变球化处理工艺：①离异共析等温球化；②预冷淬火+高温回火。2种球化处理工艺均能获得良好的球化组织和良好的综合力学性能：Rm≥1 000 MPa，Re≥700 MPa，A10=10%~14%。拉伸断口具有明显的缩颈，断口形貌呈具有典型的韧窝特征。     

Water Cooling Effects on the Microstructural Evolution and Mechanical Properties of Friction-Stir-Processed Al-6061 Alloy

Water cooling was applied during friction stir processing (FSP) of an Al-6061 alloy, and it was found that the strengthening efficiency induced by water cooling was varied, which was dependent on the initial base metal temper. As to the natural-aged Al-6061 alloy (6061-NA), the stir zone (SZ) was strengthened significantly by water cooling. Compared with the air-cooled FSP sample, the relatively high strength of the water-cooled FSP sample mainly arose from grain refinement, increased density of dislocations and large amounts of fine re-precipitated Guinier–Preston zones in the SZ. On the contrary, as to the annealed Al-6061 alloy (6061-O), the difference in the microstructural evolution between the FSP samples with and without water cooling was nonsignificant, where only finer grain morphology was observed in the water-cooled SZ, and thus the strengthening effects caused by water cooling became less.     

Ti和/或Nb对高温合金25Cr37Ni0.6Nb组织和力学性能的影响

研究了150 kg真空感应炉冶炼并轧成30 mm板的0.05C-25Cr-37Ni-0.6Nb(0.6Nb),0.05C-25Cr-37Ni-0.6Nb-0.6Ti(0.6Nb-0.6Ti)和0.05C-25Cr-37Ni-1.8Nb(1.8Nb)3组合金1160~1220℃ 1 h空冷固溶处理的组织和性能。结果表明,与0.6Nb合金相比加Ti的(0.6Nb-0.6Ti)合金的晶粒明显粗化,析出相主要为微米级Ti(CN),室温强度降低,760℃蠕变性能降低;增加Nb含量的1.8Nb合金的晶粒细化,析出相主要为纳米级Nb(CN),室温强度和蠕变性能没有明显变化。     

Effect of tempering on mechanical properties of 25Co15Ni11Cr2MoE steel

The change rule of mechanical properties and impact fracture morphologies of a high Co- Ni secondary hardening ultra- high strength 25Co15Ni11Cr2MoE steel tempered at 200-750?? after quenched was studied by mechanical properties test and microstructure analysis such as optical microscope(OM) and scanning electron microscope(SEM). The results show that experimental steel after quenching and tempering has a remarkable secondary hardening effect. After tempered at 400-495??, the hardness of experimental steel can reach and beyond the quenched hardness. In this range, tensile strength, yield strength and hardness of experimental steel increase with the tempering temperature increasing, tensile strength and hardness of experimental reach maximum (57. 3HRC and 2160MPa) after tempered at 470??, meanwhile, with the tempering temperature increasing, impact toughness of experimental steel decreases during the prophase, until reaches minimum at 430??, then increases gradually, and reaches maximum after tempered at 510??. The recommended optimum heat treatment process of 25Co15Ni11Cr2MoE steel is as follow: 950???1h oil quenching??(-73??)??1h rising back to room temperature in the air ??495???5h air cooling. At this time, the experimental steel has the best strength and toughness matching.     

Notch Impact Behavior of Oxide-Dispersion-Strengthened (ODS) Fe20Cr5Al Alloy

In this article, tensile tests as well as LS and LT notched Charpy impact tests were performed at the temperature range between 77 K (?196 °C) and 473 K (200 °C) on an oxide-dispersion-strengthened (ODS) Fe20Cr6Al0.5Y₂O₃ hot-rolled tube. The absorbed energy values in the range of high temperatures of LS notched specimens are considerably higher than those of LT notched specimens; however, such values tend to converge as temperature increases. Ductile fracture on the normal planes to RD with delaminations parallel to the tube surface was observed in the temperature range between room temperature (RT) and 473 K (200 °C). Delaminations of crack divider type were observed in LT specimens, whereas delaminations of crack arrester type were observed in LS specimens. The yttria particles in the grain boundaries and the transverse plastic anisotropy are the possible reasons why the delaminations were parallel to the tube surface.     

时效温度对马氏体沉淀硬化不锈钢0Cr15Ni5WMoVNb力学性能的影响

0Cr15Ni5WMoVNb钢(%:0.068C、14.54Cr、5.32Ni、0.88W、0.92Mo、0.20V、0.10Nb)经5 t中频感应炉+2 t真空电渣重熔炉冶炼,经锻造、热轧成Φ45 mm棒材,试样经1 000℃30 min固溶空冷+-70℃2 h冷处理后进行400～600℃4 h时效空冷。试验结果表明,在450℃时效0Cr15Ni5WMoVNb钢的强度最大,以准解理断裂为主,冲击功低为40 J,随时效温度上升,冲击功显著上升,强度下降,在510℃时效该钢有良好的强韧性,抗拉强度R_m 1300 MPa,屈服强度R_(p0.2)1100 MPa,冲击能A_(KV) 100 J。