Ni对铝热反应制备块体纳米晶Fe_3Al材料力学性能的影响

通过铝热反应熔化方法制备Ni质量分数分别为5%、10%、15%的块体纳米晶Fe3Al材料,研究材料在室温压缩和弯曲下的力学性能及硬度.结果表明,所制备材料的平均晶粒尺寸均约为21 nm;随着合金元素Ni质量分数的增加,材料的硬度和屈服强度δ0.2逐渐增大;材料在弯曲实验中均表现为脆性断裂,弯曲强度随Ni含量的增加先增大后减小,w(Ni)=10%的材料弯曲强度最大,为328.7 MPa.     

等温处理对铝热法制备的块体纳米晶Fe_3Al晶粒尺寸和硬度的影响

为研究等温处理对铝热法制备的块体纳米晶Fe3Al平均晶粒尺寸和硬度影响,对制得的材料进行800～1 200℃的等温处理.通过XRD和TEM分析材料的晶体结构和平均晶粒尺寸,用布洛维光学硬度计测定材料的维氏硬度.结果表明:等温处理前后纳米晶Fe3Al的晶体结构未发生变化,均为无序bcc结构;材料的平均晶粒尺寸约为16 nm,在等温处理之后有所长大,1 200℃等温处理8 h后,平均晶粒尺寸达到最大值20 nm;纳米晶Fe3Al的维氏硬度约为481 HV,在等温处理之后略有减小,经1 200℃等温处理8 h,维氏硬度最小值为457 HV.     

纯铜表面纳米化的微观结构演化及其力学性能研究

利用表面机械滚压处理（surface mechanical rolling treatment,SMRT）工艺在纯铜表面制备出梯度纳米结构层,获得了最表层为取向随机的纳米晶粒、亚表层的晶粒尺寸在厚度方向上呈梯度分布的结构层。采用光学显微镜、扫描电子显微镜、透射电子显微镜对微观组织进行表征,研究了晶界、位错、孪晶界等微观结构的演化。通过改变SMART工艺参数,在纯铜表面制备出不同厚度的梯度纳米结构层,对比分析了梯度纳米结构层厚度对纯铜力学性能的影响。结果表明：经SMRT后,试样距表面大约5 μm处的显微硬度高达1.56 GPa,其横截面的硬度随着距表面深度增加呈递减趋势;相比于粗晶铜,SMRT后纯铜的屈服强度提高了2倍多,而塑性损失很少,并且SMRT后纯铜的屈服强度随着梯度纳米结构层厚度的增加而提高。     

Al_2O_3/SiC纳米陶瓷复合材料的制备及力学性能

采用一次粒径分别为10nm和15nm的αAl2O3和SiC粉体为原料,制备了Al2O3/SiC纳米陶瓷复合材料·纳米SiC颗粒明显抑制Al2O3基体晶粒的长大,SiC体积分数超过4%时,材料的断裂方式由沿晶断裂变为穿晶断裂·随SiC含量的增加,Al2O3/SiC纳米复合材料的硬度增大·材料的弯曲强度和断裂韧性在SiC体积分数为5%时达到最大值·最大三点弯曲强度和断裂韧性分别为641MPa和47MPam1/2,明显高于热压单相Al2O3陶瓷(344MPa和31MPam1/2)·复合材料的强化主要来源于内晶颗粒残余应力强化和晶粒细化...     

TiN晶体尺寸与其力学性能的第一性原理研究

 纳米多晶体材料因其独特的力学性能而成为当前材料科学领域的研究热点之一,尤其是晶粒尺寸对其力学性能的影响倍受关注。本文采用基于密度泛函理论的第一性原理方法,模拟计算了晶粒尺寸为0.6387—2.332nm的TiN的力学性能,得到应力应变关系及屈服强度。计算结果表明,随着晶粒尺寸的增加,TiN的屈服强度降低,晶粒呈现软化趋势。通过对应力-应变曲线分析可知：TiN在应变5%处开始屈服,其屈服强度大约为21.5GPa;抗拉强度发生在应变约为15%时,且随着晶粒尺寸的增加,抗拉强度降低。本文对照了屈服极限的计算值和有限元方法的拟合值,讨论了实验中TiN表面的微观结构与硬度、弹性模量的关系。研究表明,TiN试样中的缺陷对其硬度和强度有很大影响。     

铜模吸铸法制备的Fe_(74)Al_4Sn_2(PSiBC)_(20)块体非晶与块体纳米晶合金

利用铜模吸铸法制备了直径Φ1.0mm和2.0mm的Fe74Al4Sn2(PSiBC)20块体非晶合金和直径2.0mm的Fe74Al4Sn2P10Si4B4C2块体纳米晶合金圆棒.利用X射线衍射、差示扫描量热仪(DSC)和差热分析仪(DTA)对Fe74Al4Sn2(PSiBC)20块体非晶合金的结构和热性质进行了测定.该非晶合金系在凝固前能够获得较大的过冷度,并具有较高的约化玻璃转变温度Tg/Tm(Tg/T1).利用透射电子显微镜(TEM)观察了制备态的Fe74Al4Sn2P10Si4B4C2纳米晶合金圆棒的结构,为非晶基体上均匀分布的尺寸10-20nm的α-Fe晶粒.合金凝固前获得较大的过冷度,较高的约化玻璃转变温度和多步晶相析出过程有利于获得块体纳米晶材料.铜模吸铸法既可制备块体非晶合金,也可制备块体纳米晶合金,是一种很有吸引力的制备块体非晶合金和块体纳米晶合金的方法,并进一步证实利用快速凝固法可以直接制备块体纳米材料.     

钎焊后自然时效对3003/6xxx/3003复合铝合金性能和组织的影响

以6xxx系铝合金为芯材,3003铝合金为两侧皮材,经熔炼、铸造、复合、热轧、冷轧及成品退火制备了厚度为1.5 mm的3层复合铝合金。在600 ℃下模拟钎焊,经空冷后进行1、5、10、15、20、25、30 d的自然时效。结果显示：复合铝合金的强度、维氏硬度在自然时效初期快速增加,20 d后上升缓慢,30 d时抗拉强度、屈服强度、芯材维氏硬度达到最大,分别为242.3 MPa、122.9 MPa、84.0;芯材晶粒尺寸钎焊后较钎焊前略微长大,经不同自然时效时间的芯材晶粒平均尺寸大小相当,表明自然时效不改变芯材晶粒的大小;钎焊后以及经自然时效之后芯材中标识出的第二相为不规则的AlFeSiMnCu相。     

铝热反应制备纳米晶Fe_3Al过程中熔体冷却的温度场模拟

利用有限元分析软件ANSYS模拟铝热反应熔化制备块体纳米晶Fe3Al过程中熔体冷却的温度场,并通过实验对结果进行验证.结果表明:熔体主要通过Cu底材的热传导进行传热.沿高度方向,距Cu底材越近,Fe3Al熔体温度越低;0.5 s前距Cu底材越近,Fe3Al熔体冷却速度越大,0.5 s后其冷却速度趋于一致.距底材越远,Fe3Al熔体的过热时间越长,净化效果越好.沿径向,整个过程中Fe3Al熔体的温度、冷却速度基本相同.测温点处计算温度和实测温度的数值基本吻合,变化规律一致.     

NiAl(Co)金属间化合物纳米晶块体材料的制备及其性能

采用机械合金化方法获得NiAl(Co)纳米晶粉末,经过热压,成功地制备出NiAl(Co)块体纳米晶材料·其晶粒尺寸约在300～480nm,致密度可达到91%以上,室温压缩屈服强度达到1250～1400MPa,是铸态NiAl合金的31～35倍,室温塑性良好,有大约13%的压缩塑性·其中Ni50Al40Co10纳米晶块体材料压缩率可达30%,而无裂纹产生;Ni50Al45Co5,在980℃高温压缩至195%无裂纹产生,变形均匀·还发现含γ′相的NiAl(Co)的双相纳米晶块体材料压缩性能优于单相NiAl(Co)纳米晶块体材料     

氨基磺酸镍体系电沉积纳米镍的力学性能及热稳定性研究

采用氨基磺酸镍体系镀镍液代替瓦特型镀镍液,应用脉冲电沉积技术,制备了平均晶粒尺寸为16.7 nm的纳米镍.在静拉伸应变速率范围(5×10-5~10-2s-1)内,纳米镍的强度和塑性均随应变速率的增加而增加,断裂形式表现为韧窝韧性断裂,获得的最高断裂强度和最大断裂延伸率分别为1 332MPa和5.31%.在退火温度为100、150和200℃保温1 h后,室温应变速率为10-3s-1时,纳米镍的强度和塑性随退火温度的升高而显著下降,原因为退火过程中晶内硫元素向晶界强烈偏聚引起材料变脆,断裂形式表现为晶间脆性断裂.XRD和TEM的观测结果表明,纳米镍在250℃退火时,晶粒发生显著长大,硬度快速下降.热分析仪测得的放热峰表明,275℃以后,大量的纳米晶粒发生异常长大.     

Effects of normal stress,surface roughness,and initial grain size on the microstructure of copper subjected to platen friction sliding deformation

The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation (PFSD) processing were investigated. In each case, the deformation microstructure was characterized and the hardness of the treated surface layer was measured to evaluate its strength. The results indicated that the thickness of the deformed layer and the hardness at any depth increased with increasing normal stress. A smaller steel platen surface roughness resulted in less microstructural refinement, whereas the microstructural refinement was enhanced by decreasing the surface roughness of the Cu sample. In the case of a very large initial grain size (d > 10 mm), a sharper transition from fine-grain microstructure to undeformed material was obtained in the treated surface layer after PFSD processing.     

球磨时间对Mo_2FeB_2基金属陶瓷组织和力学性能的影响

以Mo、FeB、Cr、Ni、Fe粉末以及少量的C粉为原料,采用行星球磨法对其球磨后烧结制备Mo2FeB2基金属陶瓷,利用扫描电镜观察球磨粉及其烧结试样的组织形貌,并测定烧结试样的孔隙度、硬度和抗弯强度,研究原料粉末球磨时间对Mo2FeB2基金属陶瓷组织和力学性能的影响。结果表明,随着球磨时间的增加,粉末粒度逐渐变小,Mo2FeB2基金属陶瓷的孔隙度明显降低,其硬度和抗弯强度明显增大,晶粒也随之细化;球磨30h原料粉末所制Mo2FeB2基金属陶瓷的综合性能最优,其硬度(HRA)达到90.2,抗弯强度达到1850MPa。     

工艺条件对钢铁废渣玻璃陶瓷显微结构的影响

通过对材料组成和结构的设计,获得了高炉渣和钢渣用量为55％－60％,抗弯强度大于300MPa,显微硬度达12GPa,耐磨性比GCr15钢高26倍的玻璃陶瓷。探讨了微晶化工艺条件对钢铁废渣玻璃陶瓷的显微结构和性能的影响,在一定工艺条件下所制备的玻璃陶瓷的晶相含量可达90％以上,晶粒大小仅0．1－0．3μm,多为等轴柱状晶,以辉石类为主晶相。     

热等静压316L不锈钢致密体的组织与性能

采用热等静压方法对气雾化316L奥氏体不锈钢粉末致密化,用箱式电阻炉对致密体进行了固溶处理,研究了固溶前后致密体的显微组织和力学性能,并对其拉伸断口形貌进行了分析．结果表明：热等静压态致密体密度接近理论全致密,内部组织为细小的奥氏体,存在较多的碳化物,抗拉强度、屈服强度分别达到595．3MPa和263．3MPa,延伸率为58．3％,硬度为HBS152．3;固溶处理使致密体强度和硬度降低,塑性增加,且随着固溶温度的提高,强度迅速降低,塑性明显提高,最佳固溶温度为1050℃;在固溶温度为1050℃和水冷的情况下,最佳保温时间为20min;固溶处理前后拉伸试样断口呈现明显的韧性断裂,固溶韧性好于固溶前的,均高于热轧态产品的韧性．     

Mg和Si质量比对6系铝合金性能的影响

6系铝合金中Mg和Si元素是主要强化元素,其中Mg和Si质量比是其成分配比中的重要参数。通过对材料微观组织、力学性能、导电性和韧性进行测试和分析,研究Mg和Si质量比对6系铝合金组织形貌和性能的影响。研究结果表明：随Mg和Si质量比的增加,6系铝合金组织中粗晶层厚度与析出相的尺寸均减小,屈服强度、抗拉强度和硬度均小幅度降低,电导率呈上升趋势,同时抗裂纹性能逐渐提高;当比值为1.30时,屈服强度为278 MPa,抗拉强度为300 MPa,维氏硬度为97.6 ,电导率可达51.86 %IACS,压溃裂纹长度约为10 mm,承受的载荷最大,吸收功最大,压溃性能最好。     

铜极薄带轧制过程中尺寸效应的研究

利用四辊异步冷轧机轧制工业纯铜极薄带,对轧制出厚度为25~300μm的轧件进行拉伸实验,发现在其力学性能方面出现了尺寸效应现象:随着厚度的减小,材料抗拉强度先增大,达到某一厚度临界值后转而减小,即存在一个厚度阈值,在此阈值之前出现加工硬化,之后转为加工软化.针对这一现象,对轧件进行机械性能检测和EBSD等观察或分析,认为极薄带出现尺寸效应的原因是:随着轧件厚度的减薄,胞壁沿厚度方向尺寸大幅度减小,位错向胞壁迁移距离减小,异号位错在胞壁处湮灭,导致抗拉强度降低.     

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn–1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples’ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness (Hv = 122 MPa), compressive yield strength (382 MPa), tensile yield strength (332 MPa), ultimate tensile strength (370 MPa), and elongation (9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall–Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.     

焊接速度对自适应双轴肩搅拌摩擦焊接Al–Mg合金接头微观组织和机械性能的影响

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.     

Mechanical properties of electroformed copper layers with gradient microstructure

The electroformed copper layer with gradient microstructure was prepared using the ultrasonic technique. The microstructure of the electroformed copper layer was observed by using an optical microscope (OM) and a scanning electron microscope (SEM). The preferred orientations of the layer were characterized by X-ray diffraction (XRD). The mechanical properties were evaluated with a Vicker’s hardness tester and a tensile tester. It is found the gradient microstructure consists of two main parts: the outer part (faraway substrate) with columnar crystals and the inner part (nearby substrate) with equiaxed grains. The Cu-(220) preferred orientation increases with the increasing thickness of the copper layer. The test results show that the microhardness of the electroformed copper layer decreases with increasing grain size along the growth direction and presents a gradient distribution. The tensile strength of the outer part of the electroformed copper layer is higher than that of the inner part but at the cost of ductility. Meanwhile, the integral mechanical properties of the electroformed copper with gradient microstructure are significantly improved in comparison with the pure copper deposit.