Y2O3添加量对Al2O3/ZrO2共晶陶瓷显微组织及力学性能的影响

为探索第三组元Y₂O₃添加对Al₂O₃/ZrO₂共晶陶瓷显微组织与机械性能的影响,本文利用低温度梯度的高温熔凝法制备了直径为20 mm的Al₂O₃/ZrO₂(Y₂O₃)共晶陶瓷块体,采用SEM、EDS及XRD技术对共晶陶瓷进行微结构分析,并利用维氏压痕法对其硬度和断裂韧性进行测试。SEM结果表明,凝固组织由群集的共晶团结构组成,随着Y₂O₃添加量的增加,共晶团形态由胞状转变为枝晶状,内部相间距在1~2 μm范围内变化。力学测试表明,Y₂O₃摩尔分数小于1.1%时,由于组织内部存在低硬度m-ZrO₂及微裂纹缺陷,故陶瓷硬度较低,约为(9.53±0.22 )GPa;当Y₂O₃摩尔分数为1.1%时,陶瓷硬度最大,约为(18.05±0.27)GPa;当Y₂O₃的摩尔分数大于1.1%时,由于共晶团边界区内气孔缺陷及粗大组织增多,引起陶瓷硬度值略有下降。低Y₂O₃摩尔分数添加时,陶瓷断裂韧性相对较高,约为(6.30±0.16)MPa·m^1/2,这与其内部存在大量微裂纹缺陷有关;随着Y₂O₃添加量的增加,陶瓷的微裂纹数量减少、边界区内缺陷增多,断裂韧性降低。     

Al2O3/Ni金属陶瓷力学性能和介电性能的研究

以热压烧结的方法制备了Al2O3/Ni金属陶瓷,探讨了Al2O3/Ni金属陶瓷显微结构、力学性能及微波介电性能随Ni粒子含量变化的规律.结果表明,在垂直于压力方向上,Ni粒子有明显的受压拉伸现象;当Ni粒子含量从5%(体积分数)增加至20%(体积分数)时,金属陶瓷中Ni粒子的分布由孤立向部分桥连方式转变.随Ni粒子含量的增加,金属陶瓷致密度略有下降,抗弯强度明显降低.与纯氧化铝陶瓷相比,含20%(体积分数)Ni粒子Al2O3/Ni金属陶瓷的断裂韧性提高了50%左右,达到6.4MPa·m1/2.复介电常数测试结果表明,在8.2～12.4GHz频率范围内,金属陶瓷复介电常数的实部和损耗随Ni粒子含量的增加逐渐上升.当Ni粒子含量达到20%(体积分数)时,由于Ni粒子之间的部分桥连现象而使介电常数虚部在一定频段出现负值.     

热处理对铸造Ti15-3合金显微组织和力学性能的影响

借助光学显微分析、ＴＥＭ和ＳＥＭ分析手段研究了不同热处理工艺对Ｔｉ１５－３合金显微组织和力学性能的影响。结果表明：合金在铸态时的组织特征为粗大的β相,由于合金中没有析出相的弥散强化作用,因而合金的强度低,在不同温度时效处理后,在晶内和晶界析出α相,随着时效温度和时效时间的增加,析出相不断粗化,与铸态相比,合金时效后强度大幅度提高而处伸率大幅度下降,在变形过程中,合金中的位错在析出相周围形成缠结,合     

Effect of Zr on microstructure and mechanical properties of the Al–Cu–Er alloy

ABSTRACT

The microstructure and mechanical properties of the Al–4Cu–2.7Er–0.3Zr alloy were investigated. The precipitates of the L1₂ structured phase with sizes 37?±?12?nm were formed in lines and homogenously distributed inside the aluminium matrix after annealing at 605°C for 1?h. The as-rolled Al–4Cu–2.7Er–0.3Zr alloy developed an increased hardness after 1?h annealing at 100–550°C and 0.5–6?h annealing at 150–250°C due to precipitation of the Al₃(Er,Zr) phase. Addition of Zirconium improved the tensile properties relative to those of the Zr-free alloy by approximately 20?MPa: yield strength?=?273–296?MPa and ultimate tensile strength?=?296–328?MPa in the alloys annealed at 100–150°C.     

Surface modification of Cr3C2–NiCr cermet coatings by direct diode laser

Thermal spraying has emerged as an important tool of increasingly sophisticated surface engineering technology, and it is being used widely to repair and surface modification in metallic parts. The Cr₃C₂–NiCr sprayed coatings are frequently used as wear resistant coatings against abrasion and erosion at high temperature up to 1173 K, and in corrosive environments. Hardness and microstructure of Cr₃C₂–NiCr cermet coatings fused by direct diode laser process was compared with that formed by high-velocity oxygen fuel spraying (HVOF) process. The effect of beam characteristics (power density, power, scanning speed, etc.) was examined on the surface modification of sprayed coatings. In this study, we treated Cr₃C₂–25%NiCr cermet coatings by laser irradiation process and examined its hardness compared with that formed by HVOF process. Consequently, the average hardness of laser-treated Cr₃C₂–25%NiCr cermet coatings has been found out to be higher than that of HVOF coatings. Laser remelting improved markedly the wear resistance of HVOF sprayed Cr₃C₂–25%NiCr cermet coatings.     

石墨烯/纳米Al2O3增韧Ti(C,N)基金属陶瓷的力学及摩擦磨损性能

采用真空热压烧结工艺制备了石墨烯(GNPs)和纳米Al₂O₃增韧的Ti(C,N)基金属陶瓷复合刀具材料(TAG)。研究了GNPs和纳米Al₂O₃对复合陶瓷材料微观结构、力学性能和摩擦磨损性能的影响。研究表明,GNPs和纳米Al₂O₃的添加对复合陶瓷材料的力学性能有明显的提高,当GNPs和纳米Al₂O₃含量(质量分数)为1%和5%时,复合刀具陶瓷材料(TA5G1)综合力学性能最优,其硬度、抗弯强度和断裂韧性分别为21.50 GPa、810.80 MPa和10.51 MPa·m^1/2。研究了复合刀具材料的摩擦磨损性能和磨损机理,研究结果表明,在TAG复合刀具材料中,TA5G1的摩擦磨损性能最优,其摩擦系数和磨损率分别为0.338和4.921×10^-6 mm³/(N·m),复合刀具材料的主要磨损形式为磨粒磨损和黏着磨损。     

Deformation behaviour and microstructure of a 20% Al2O3 reinforced 6061 Al composite

Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s⁻¹. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms. The 20% Al₂O₃/6061 Al composite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the 10% Al₂O₃/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the three point bending failure specimens.     

Study on microstructure and properties of centrifugal casting 35Cr45NiNb+MA furnace tubes during service

In the present study, the microstructure evolution of 35Cr45NiNb+MA ethylene cracking furnace tubes during service and its effect on the properties were investigated. According to the results, in the early stage of service, the skeletal M₇C₃ and vermicular NbC were transformed into blocky M₂₃C₆ and G phase (Ni₁₆Nb₆Si₇), respectively, accompanied with many dispersed M₂₃C₆ secondary carbides. With the extension of service time, M₂₃C₆ carbides on the grain boundaries were transformed into M₇C₃ with high stacking fault structure and coarsened, and the blocky G phase was transformed into granular NbC. The yield strength and ultimate tensile strength of the aging furnace tubes decreased by 9%-18%, yet the elongation after fracture decreased significantly from 10.0%-14.0% to 3.0%-5.0%. The hardness of the carburized zone of the carburized tubes increased by 10%-17%, and the rupture time decreased by 45%-75% under the test condition of 1100℃ and 16MPa. Finally, the evolution map was summarized.     

Effect of metal coating of reinforcements on the microstructure and mechanical properties of Al-Al2O3 nanocomposites

The effects of various methods of reinforcement modification on the microstructure and mechanical properties of Al–Al₂O₃ nanocomposites were investigated. Alumina nanoparticles were modified by electroless deposition of Cu, Ni and Co. Subsequently, aluminium matrix nanocomposites reinforced with uncoated and coated nanoparticles were produced by the stir casting method. The results of microstructural analysis showed improved wettability of coated nanoparticles in the molten aluminium alloy. Furthermore, coated nanoparticles exhibited a more desirable interface with the matrix and were homogenously distributed within it. The mechanical properties of the nanocomposites were improving significantly when coated nanoparticles were used as reinforcements. Among the reinforcement modification methods, Ni-coating was recognised as being more effective for improving the mechanical properties of Al–Al₂O₃ nanocomposites.     

Fe含量对Al-1.04wt.%Mg-0.64wt.%Si-0.23wt.%Cu合金析出相、力学性能和腐蚀性能的影响

Fe含量对于铝合金的熔炼成本、成形性能和使用性能具有重要影响,本文研究了 Fe含量(质量分数)对AlMg1SiCu合金析出相、力学性能和腐蚀性能的影响,并探讨了 Fe含量对性能的影响机制.结果表明,随着Fe含量由0.27％增加至1.44％,试样中的主要富铁相变化规律为:针状β-Al9Fe2Si2 →汉字状α-Al17 Fe3.2 Mn0.8 Si2 →短棒状Fe2Al3Si3.Fe含量由0.27％增加到1.21％时,试样的平均晶粒尺寸由173 μm减小到122 μm,继续提高Fe含量则平均晶粒尺寸增大.在本文Fe含量范围内,试样的屈服强度基本不变,但抗拉强度和断后伸长率随着Fe含量的增加而显著增加,当Fe含量超过1.21％时略有下降,其原因与富铁相的变化规律有关.试样的腐蚀速率与试样中主要富铁相的种类和数量有关,试样的自腐蚀电位随着Fe含量的增加先增大后减小,腐蚀电流随着Fe含量的增加逐渐增大.综合考虑力学和腐蚀性能因素,AlMg1SiCu合金合适的Fe含量约为0.50％.     

Al2O3/Ni金属陶瓷显微结构和力学性能的研究

采用包裹工艺和热压工艺制备了Al2O3/Ni金属陶瓷.在1450°C热压Ni包裹Al2O3复合粉体得到相对密度＞98%的金属陶瓷,当温度＞1400°C时,随着Ni含量的增加致密度下降.Ni颗粒位于三角晶界,随着含量的增加,断裂方式由沿晶转为穿晶断裂;在A12O3基体中引入Ni颗粒能够降低晶粒尺寸,提高强度和韧性.与单相Al2O3的力学性能相比,综合力学性能较好的NA4金属陶瓷的抗弯强度和断裂韧性分别提高了19%和35%,分析了金属陶瓷的增强增韧机制.     

Effect of microstructure morphology on mechanical properties of quenching and partitioning steel

In order to illuminate the relationship between microstructure morphology and final properties of the quenching and partitioning(Q&P) steel, the samples with different microstructure morphology (equiaxed and lamellar) and same volume fraction of each phase are obtained by controlling the initial microstructure and Q&P heat treatment. Because of the feature of microstructure morphology, a large yield ratio and total elongation are obtained in the lamellar sample though yield strength and ultimate tensile strength are relatively lower than that of equiaxed sample. Moreover, the lamellar sample produces a continuous work-hardening rate and better the fracture toughness compared to the equiaxed sample. Thus the lamellar sample is more suitable to be used as automotive structural components.     

Effect of Nb2O5 on the microstructure and mechanical properties of TiAl based composites produced by hot pressing

In situ composites of TiAl reinforced with Al₂O₃ particles are successfully synthesized from an elemental powder mixture of Ti, Al and Nb₂O₅ by the hot-press-assisted reaction synthesis (HPRS) method. The as-prepared composites are mainly composed of TiAl, Al₂O₃, NbAl₃, as well as small amounts of the Ti₃Al phase. The in situ formed fine Al₂O₃ particles tend to disperse on the matrix grain boundaries of TiAl resulting in an excellent combination of matrix grain refinement and uniform Al₂O₃ distribution in the composites. The Rockwell hardness and densities of TiAl based composites increase gradually with increasing Nb₂O₅ content, and the flexural strength and fracture toughness of the composites have the maximum values of 634 MPa and 9.78 MPa m^1/2, respectively, when the Nb₂O₅ content reaches 6.62 wt.%. The strengthening mechanism was also discussed.     

Effect of the heat treatment on the microstructure and mechanical properties of medium-Mn-steels

ABSTRACT

The heat-treatment (HT) schedule and selected annealing parameters have a substantial effect on the microstructure and mechanical properties of medium-Mn-steels. The structure morphology depends on the fact, whether the austenite-reverted transformation takes place from deformed (one-step HT) or non-deformed (two-step HT) microstructures. Depending on the intercritical annealing temperature, the stability of the retained austenite can be altered to a large extent. As a result, the mechanical properties can be adjusted from high strength with excellent ductility to very high strength with reasonable ductility. The present contribution, therefore, elucidates the dependence of the microstructural characteristics and material behaviour on the HT parameters for medium-Mn alloy compositions with different Mn-contents.

This paper is part of a Thematic Issue on Medium Manganese Steels.     

Ti添加对WC-Ni3Al硬质合金微观组织与力学性能的影响

为提高WC-Ni₃Al硬质合金的力学性能，采用放电等离子烧结制备Ti掺杂的WC-Ni₃Al硬质合金，并研究不同Ti添加量对WC-Ni₃Al硬质合金微观组织和力学性能的影响。结果表明: Ti的添加减小WC-Ni₃Al块体样品中反应生成的少量Al₂O₃的尺寸，并且使Al₂O₃的分布更加均匀。一方面，小尺寸的Al₂O₃与原位生成的(Ti, W)C协同提高WC-Ni₃Al块体样品的硬度；另一方面，适量Ti的添加还提高WC-Ni₃Al硬质合金的断裂韧度，这是由于原位生成的(Ti, W)C与WC有较好的界面结合，增加对裂纹扩展的桥接与偏转作用。当添加3%(质量分数)的Ti时，WC-Ni₃Al硬质合金获得了优异的力学性能，硬度和断裂韧度分别为(19.29±0.18) GPa和(13.14±0.24) MPa·m^1/2。     

Cr3C2粒径对等离子堆焊铁基合金层组织与耐磨性能的影响

在低碳钢表面利用等离子堆焊技术分别制备Fe50堆焊层及添加40％(质量分数)微米和纳米Cr₃C₂的(Fe50+40%微米/纳米Cr₃C₂)复合堆焊层,比较研究添加不同粒径的Cr₃C₂对Fe50合金堆焊层的显微组织与磨损性能的影响。采用X射线衍射仪(XRD)分析堆焊层的相组成,利用扫描电镜(SEM)和能谱分析仪(EDS)观察堆焊层的显微组织形貌及微区成分,通过显微硬度计测试了堆焊层的硬度分布,使用滑动磨损及冲击磨损试验机分别考察了复合堆焊层的磨损性能。结果表明:Fe50等离子堆焊层组织主要由柱状晶α-Fe及其间的网状共晶α-Fe+Cr₂₃C₆组成;而Fe+40%微米/纳米Cr₃C₂堆焊层凝固方式为过共晶,由大量的先共晶碳化物及其间细密、均匀的枝晶与共晶组织组成,并增加了γ-Fe、Cr₇C₃和未熔Cr₃C₂等相;但Fe+40%纳米Cr₃C₂涂层比Fe+40%微米Cr₃C₂涂层析出更多且细小、致密的先共晶碳化物。与Fe50等离子堆焊涂层相比,Fe+40%微米Cr₃C₂涂层的显微硬度、滑动磨损性能及冲击磨损性能分别提高了21%、1.5倍和0.8倍;而Fe+40%纳米Cr₃C₂涂层的显微硬度、滑动磨损性能及冲击磨损性能则分别提高了34.1%、2.4倍和1.7倍,表面的犁沟和剥落及塑性变形明显减少,耐磨性能显著提高。因此,添加纳米Cr₃C₂颗粒可以显著细化铁基合金等离子堆焊层的显微组织并提升其耐磨性能。     

Effect of Mo on microstructure and mechanical properties of bulk nanocrystalline Fe3Al materials prepared by aluminothermic reaction

Abstract

Bulk nanocrystalline Fe₃Al based materials with 5, 10 and 15 wt-%Mo were prepared by aluminothermic reaction. The microstructure and mechanical properties of the materials were investigated. It was shown that the materials consisted of a nanocrystalline matrix phase that was composed of Fe, Al and Mo and a little Al₂O₃ contamination phase. The nanocrystalline phase had a disordered bcc crystal structure. Average grain sizes of the nanocrystalline phase of the materials with 5, 10 and 15 wt-%Mo were 19, 31 and 24 nm respectively and that of the material with 5 wt-%Mo was the smallest. The materials with 10 and 15 wt-%Mo exhibited brittle behaviour in compression, whereas the material with 5 wt-%Mo had a large plastic deformation. The material with 5 wt-%Mo had the highest bending strength and the lowest compressive yield strength.     

纤维表面处理对C/C复合材料组织与性能的影响

采用CVI涂层和400℃空气氧化技术对炭纤维进行表面处理,借助偏光显微镜(PLM)、扫描电镜(SEM)和弯曲性能测试研究了炭纤维表面处理对2D中间相沥青基炭/炭复合材料的组织结构与弯曲性能的影响.结果表明:两种表面处理的材料均具有韧性断裂特征,CVI涂层表面处理后材料的"假塑性效应"更为显著,但是其抗弯强度较低,基体炭的组织结构为具有光学活性的热解炭和中间相沥青炭的流线型、广域流线型组织,材料内部形成多层次的界面结构,在断裂破坏过程中,主要发生基体内聚破坏;400℃空气氧化表面处理的材料的基体炭的组织结构为中间相沥青炭的小域、广域流线型组织,材料在断裂破坏过程中,表现为混合破坏,即基体内聚破坏和界面粘结破坏同时发生.     

Effects of TiO2 doping on microstructure and properties of directed laser deposition alumina/aluminum titanate composites

ABSTRACT

Al₂O₃-based composite ceramics have excellent high temperature performance and are ideal materials for preparing hot end components. However, poor fracture toughness and thermal shock resistance limit its applications. Based on the excellent low thermal expansion characteristics and thermal shock resistance of Al₂TiO₅ ceramic, different composition ratios of Al₂O₃/Al₂TiO₅ composite ceramics were prepared by directed laser deposition (DLD) technology. Effects of TiO₂ doping amount on microstructure and properties of the composite ceramics were investigated. Results show that α-Al₂O₃ phase is discretely distributed in the continuous aluminum titanate matrix when TiO₂ doping amount between 2 and 30?mol%. With the increase of TiO₂ doping amount, content of Al₂O₃ gradually decreases and its morphology changes from cellular to dendritic. When TiO₂ doping amount reaches 43.9?mol%, the microstructure transforms into fine Al₂TiO₅/Al₆Ti₂O₁₃ eutectic structure. Property test results show that Al₂O₃/Al₂TiO₅ composite ceramics have good comprehensive mechanical properties when TiO₂ doping amount between 2 and 6?mol%.     

Ti2AlNb合金构件全流程模拟及组织性能预测

金属构件的塑性加工不仅需要控制其形状尺寸,还要调控其微观组织和力学性能,以获得满足服役要求的产品。构件成形结束后,常需要通过热处理工艺调控其组织和性能,但由于成形过程中的变形参数影响其热处理前的微观组织,因此,也影响到其热处理过程的组织演变,进而影响构件的服役性能,导致热处理调控更加复杂。本文基于机器学习的方法,考虑变形参数对热处理的影响,建立了Ti₂AlNb合金构件高温成形过程微观组织和力学性能的预测模型,并与有限元模拟软件结合,建立了Ti₂AlNb合金构件成形-热处理的全流程模拟方法。本文通过该方法对Ti₂AlNb管材高温压制-时效处理工艺进行了全流程的模拟,模拟结果表明变形和热处理参数均会对成形构件的组织和力学性能产生影响。进而通过成形和热处理实验对模拟结果进行了验证,模拟结果与实验结果的一致性较好。说明通过该方法,可以实现构件成形-热处理全流程的模拟和组织-性能预测,可用于指导加工工艺的制定。