喷射成形ZA35合金的高温磨损行为

采用喷射成形快速凝固技术制备了ZA35-3.5Mn耐磨合金,分析了合金的微观组织,利用摩擦磨损实验研究了合金的耐磨性。结果表明:喷射成形合金具有比铸造合金更细小的微观组织,摩擦因数随温度升高缓慢增加,其摩擦特性比较稳定,是一种比较理想的耐磨材料,具有比铸造合金更高的耐磨性和减磨性。喷射成形合金的磨损失效形式主要是磨粒磨损和疲劳磨损,铸造合金的磨损失效形式主要是磨粒磨损、粘着磨损和部分氧化磨损。     

不同铸造工艺制备A356-CNT纳米复合材料的摩擦学行为（英文）

研究液态成形和半固态成形法制备的A356铝合金整体铸件和A356-CNT纳米复合铸造件的摩擦学行为。采用熔体搅拌、流变铸造、搅拌铸造、复合铸造等不同工艺制备样品。研究碳纳米管(CNTs)的加入、铸造工艺和施加载荷对磨损性能和磨损机理的影响。结果表明,添加碳纳米管显著降低了纳米复合材料的磨损量、磨损率和摩擦因数。铸造工艺由液态成形变为半固态成形,和初相含量的增加是提高合金尤其是纳米复合合金样品耐磨性能的两个主要因素。此外,研究还发现液态成形和半固态成形两种方法制备的整体铸件其主要磨损机理分别是粘着磨损和剥层磨损。然而,无论制备工艺如何,磨粒磨损是纳米复合材料的主要磨损机理。     

Nb对喷射成形M3型高速钢组织和性能的影响

为了利用NbC的高硬度和高热稳定性,并避免其在凝固过程中的过分长大,采用喷射成形快速凝固技术制备了M3型高速钢和以Nb代V的M3型高速钢.利用SEM,EDX和XRD等方法研究了Nb对喷射成形M3型高速钢沉积态组织的影响;利用SRV高温摩擦磨损试验机和三维白光干涉表面形貌仪研究了Nb对喷射成形M3型高速钢摩擦磨损性能的影响.结果表明,用等原子分数的Nb替代V,可大幅增加沉积态中一次MC型碳化物.减少一次M₂C型碳化物,同时由于喷射成形高冷速的作用,使得MC碳化物尺寸减小,分布更弥散:这些MC型碳化物的存在是M3型高速钢的抗磨粒磨损性能提高的主要原因,但其对抗氧化性能并无贡献,在高载荷时抗氧化剥落磨损能力增加不明显;Nb对提高M3高速钢回火稳定性也有明显的作用.     

喷射沉积Zn-40Al-2Cu合金微观形貌和摩擦磨损性能

通过SEM和TEM的观察发现,喷射沉积制备的Zn-40Al-2Cu合金沉积坯具有细小均匀的微观组织结构,无严重偏析.结合XRD分析可知,合金组成主要为片状珠光体的α η片层状共析组织以及少量弥散分布的纳米级富Cu相ε沉淀颗粒.通过挤压和热处理工艺,可以完全消除沉积过程中形成的大量孔洞,显著改善合金的力学性能.摩擦试验发现.Zn-40Al-2Cu合金的摩擦因数随着摩擦荷载的增加而减小,随着摩擦速度的增大而增大.当载荷较低时,主要呈现犁削磨损,而载荷较大时,碾压磨损和粘着磨损占主导地位.与普通铸态合金相比,喷射沉积 挤压 热处理大大提高了合金的耐磨性能.     

粉末注射成形制备SiCP/Cu复合材料及其摩擦磨损性能研究

采用粉末注射成形技术制备SiCP/Cu复合材料零件,研究了该复合材料的粉末注射成形工艺过程,获得了理想SiCP/Cu复合材料注射成形零件,并对该复合材料进行摩擦磨损试验.结果表明,SiCP的加入改善了材料的摩擦学性能,摩擦系数随滑动时间的延长而增加得较为平缓;含10％SiCP的复合材料磨损表面的粘着和塑性变形程度轻,有一定的磨粒磨损;含15％SiCP的该复合材料磨损表面呈典型磨粒磨损;该复合材料磨损表面存在白亮色的致密机械混合层,同时磨损试验的偶件40Cr钢环表面也被犁削而形成了平行的条纹;该复合材料磨损表面含有Cu、Si、C、Fe和O元素,这增加了钢环表面转移过来的Fe元素和表面摩擦发热造成的氧化而带来的O元素.     

粉末冶金高铝锌基合金的摩擦磨损特性的研究

采用传统粉末冶金工艺,即以纯金属粉末为原料、在空气气氛中用液相烧结的方法制备了高铝锌基台金.并对其摩擦磨损特性进行了初步研究.结果表明,较佳的烧结工艺为(425～430)℃×(4～5)h,用该工艺制备均粉末冶金高铝锌基合金具有良好的耐磨性;机油润滑时的磨损机制是犁削、辗压和粘着.     

喷射成形及轧制Cr12MoV钢的微观组织与摩擦学性能研究

研究了常规铸造工艺,喷射成形工艺以及喷射成形后轧制等工艺制备的Cr12MoV钢的微观组织和摩擦学性能。结果表明,喷射成形工艺与常规铸造相比,制备的合金成分更加均匀,晶粒更加细小。而后的轧制工艺进一步改善了材料的微观组织。与常规工艺相比其碳化物颗粒的尺寸大大降低,耐磨性能得到了大幅度地提高。且提高幅度随着轧制量的增加而增加。     

铌对喷射成形M3:2高速钢组织和耐磨性的影响

研究了Nb对喷射成形高速钢M3:2组织和硬度的影响,并对含Nb喷射成形高速钢在不同温度下的摩擦行为进行了研究。结果表明,Nb可以使一次MC型碳化物变得更细小、球形度更好,M2C片层厚度变薄,有利于高速钢回火过程中的二次析出,提高其回火后的硬度。0.5 %Nb的添加可显著提高喷射成形M3:2高速钢的耐磨性。常温（20 ℃）时高速钢的磨损机制主要为磨粒磨损;中温（300 ℃）时,磨损机制则以粘着磨损为主,氧化磨损增加;高温（500 ℃）时,主要以氧化磨损为主。     

喷射成形Al22Si5Fe3Cu1Mg的高温耐磨机制

采用常规铸造和喷射成形两种工艺制造Al22Si5Fe3Cu1Mg高硅铝合金,研究磨损温度对合金摩擦行为和磨损机理的影响。结果表明:由于喷射成形高硅铝合金具有组织细小、成分均匀等特征,在磨擦过程中表现出更好的抗磨损性能。合金的磨损机制随着温度的升高而发生转变,低于临界温度时为磨粒和黏着磨损混合形式,高于临界温度后转变为剥层磨损。合金在高温下磨擦时,由于氧化速度较快,形成的氧化物改善合金的抗磨损性能,但存在一个临界温度,当超过临界温度时,两种工艺下的合金均由轻微磨粒和黏着磨损混合形式转变为严重的剥层磨损,喷射成形合金在不同高温下的抗磨损性能均显著优于铸造合金的,且其磨损机制转变临界温度比常规铸造合金的高约100℃。     

喷射成形Al-8.0Si-4.0Cu-0.5Mg合金的组织及性能

采用喷射成形技术制备了Al-8.0Si-4．0Cu-0．5Mg合金棒材,分析了该合金的组织,研究了台金成形过程中孔洞及疏松的形成情况,测量了合金的力学性能及摩擦性能。结果表明,喷射成形工艺制备的合金具有细小均匀的微观组织结构,固溶、时效处理能够得到良好的弥散强化,具有良好的性能。     

Synthesis of W-3 wt% Mn-2 wt% VC composites by high energy milling and sintering

A W-3 wt% Mn matrix alloy reinforced with 2 wt% of 24 h pre-milled VC particles were synthesized via high energy milling for 3 h, 6 h, 12 h, 24 h and then sintered at 1300 °C. The W-3 wt% Mn alloy was also prepared by high energy milling of a powder blend of W-3 wt% Mn for 6 h. Effects of milling duration as well as Mn and VC addition on the microstructural and mechanical properties of the W-3 wt% Mn-2 wt% VC composite powders and sintered samples were investigated. Microstructural characterizations of the composite powders and sintered samples were carried out via SEM and XRD analyses. Density measurements and hardness measurements of the sintered samples were also carried out. While the relative density increased from 92.4% for the sintered W-3 wt% Mn matrix to 97.8% for the sintered W-3 wt% Mn-2 wt% VC composite milled for 24 h, there was an increase of ～85% in hardness values for the W-3 wt% Mn-2 wt% VC samples milled for 24 h.     

Characterization Investigations of 2 wt% LaB6 Particulate-Reinforced Al-7 wt% Si Matrix Composites Fabricated by Powder Metallurgy Methods

Metals and Materials International - In this study, first of all, sub-micron LaB6 reinforcing particles were synthesized in the size range of 100–500 nm via mechanochemical synthesis...     

Precipitation in 18 wt% Ni maraging steel of grade 350

The evolution of precipitates in maraging steel of grade 350 was studied using the complementary techniques of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). These investigations revealed that ageing the steel at 703 K involved a rhombohedral distortion of the supersaturated b.c.c. martensite accompanied by the appearance of diffuse ω-like structures. This was followed by the appearance of well-defined ω particles containing chemical order. At the ageing temperature of 783 K, Ni₃(Ti, Mo) precipitates were the first to appear with a growth exponent of 1/3. The values of the Porod exponent obtained from the SAXS profiles indicated that the ω particles, formed below 723 K, had diffuse interfaces up to an ageing time of 48 h. On the other hand, Ni₃(Ti, Mo) precipitates, formed above 723 K, developed sharp interfaces in just about an hour. Also, the steel exhibited scaling in phase separation both at 703 and 783 K, but only during the early stages. Through this study it was established that, at temperatures of ageing less than 723 K, evolution of ω particles takes place through the collapse of the unstable b.c.c. lattice and, at temperatures above 723 K, precipitation of A₃B type of phases through the mechanism of clustering and ordering of atomic species. Sharp interfaces develop rather quickly when the mechanism of precipitation involves development and amplification of a concentration wave alone as in the nucleation of Ni₃(Ti, Mo) at 783 K than when an interplay of both the displacement and concentration waves is required as in the evolution of ω at 703 K. These results indicate towards the possibility of existence of two separate time–temperature–transformation (TTT) curves, one for the evolution of ω-phase and another for nucleation and growth of Ni₃(Ti, Mo).     

直流条件下W-15wt%Cu电接触材料燃弧特性研究

研究了W-15wt%Cu电接触材料在直流条件电弧作用下电极表面元素分布、材料微观组织形貌;探讨了电接触材料在直流电弧作用下的转移和腐蚀机理。结果表明:直流电弧引起阳极表面熔化、Cu离子向阴极转移并在阴极表面沉积;金属氧化物在电弧高温作用下分解成单元素,吸收了电弧能,有利于灭弧;同时W颗粒悬浮在阳极Cu微小熔池中,增加了熔融Cu的粘度,有利于降低Cu熔滴的飞溅,减少了电弧烧损。W-15wt%Cu复合电接触材料显示出良好的综合电性能。     

High temperature deformation of a submicron grained Al-12 wt% Ti alloy

Compressive deformation behavior of a MA Al-12wt%Ti alloy has been studied at 623–773 K with strain rates from 4 × 10⁻⁵ to 1 × 10⁻¹s⁻¹. A high stress exponent was observed in the stress dependence of strain rate. By assuming that the presence of a threshold stress is the cause of the high stress exponent, the experimental data were analyzed and compared with existing models. The creep behavior of this alloy is found similar to the dispersion strengthened Al-Al₂O₃ alloys. It is suggested that the high temperature deformation of this alloy is mainly governed by the fine carbide and oxide strengthened aluminum matrix, which can be described by lattice-diffusion controlled creep with a “constant structure” [11]. In addition, a strong temperature dependence of the threshold stress was observed. It might be related to certain grain boundary processes and/or thermally activated deformation of strengthening particles.     

Al-4.5Cu柱状晶的顺流生长

利用自行研制的电磁泵驱动液流定向凝固装置,在给定冷却条件下,系统地研究了液相流动对Al-4.5Cu合金柱状晶生长方向的影响。发现：低生长速度区,柱状晶以胞状生长方式顺流偏转;高生长速度区,柱状晶以枝晶方式生长,随液流速度由小增大,经历了等轴晶生长、迎流生长、近垂直生长及顺流生长四种变化。     

Mg-5wt％Sn合金铸态和时效态的高温蠕变性能

通过压缩蠕变试验研究了铸态和时效态(T6)Mg-5wt%Sn合金在应力为25MPa,温度为150、175和200℃下的高温蠕变性能,并测试了室温拉伸性能.结果表明,时效处理后的压蠕变性能有很大的提高,时效态合金室温抗拉强度也有明显改善.时效态合金高温压缩蠕变性能的提高和室温强度的改善与Mg2Sn弥散析出强化有关.     

Twinned Martensitic Substructure in a Water Quenched Fe-1.0 wt% C Alloy

A Fe-1.0 wt% C alloy was quenched into water from 1100 °C, leading to lath martensite and plate martensite of body-centered tetragonal structure. Both these two martensites have the twinned substructure that generates mirror symmetric diffraction patterns with extra diffraction spots around n /3 (112). The twinned substructure has the origin from twinned martensitic variants, namely twin-related crystals separated by {110}, rather than {112}<111> deformation twins. Tetragonality effect on the electron double diffraction of twinned variants was discussed.     

过冷Cu-Pb偏晶合金的凝固热力学分析

采用熔融玻璃净化和循环过热相结合的方法实验研究了Cu-34.15%Pb偏晶合金在0~204K的宽过冷度区间的冷却曲线。实验结果表明,Cu-34.15%Pb偏晶合金在较小过冷时只有一次再辉,较大过冷时有两次再辉,偏晶反应中液相L2恒为初生相。根据经典形核理论和冷却曲线讨论了偏晶合金的两相竞争形核规律,并推断出Cu-Pb合金偏晶反应中液液相变焓ΔHL的取值范围为5×108~1.8375×109J.m-3。研究发现,ΔHL的大小对于偏晶反应中的α相和L2相的两相竞争形核起着至关重要的作用,需要精确地测定。     

热压法制备20％Grp／6061Al复合材料及其摩擦磨损特性研究

采用快速升温热压法制备了20%Grp/6061Al(质量分数,下同)复合材料并研究其摩擦磨损特性,通过光学显微镜和SEM分别观察了样品的组织结构及磨痕形貌,采用XRD分析了复合材料的相组成.研究表明快速升温热压能避免有害的界面反应,得到石墨颗粒分布均匀、界面干净且结合良好的Grp/6061Al复合材料,复合材料具有良好的摩擦磨损性能,T6处理能显著降低复合材料的摩擦系数和磨损率.在60 r/m转速、1 N～7 N载荷下,复合材料的摩擦系数随载荷的增大而减少,磨损量增大.T6热处理强化了界面结合,有利于石墨膜形成,降低了复合材料的摩擦系数,也显著减少了磨损率.热处理后,复合材料摩擦系数可达到0.16,磨损量平均减幅达50%,采用的最大载荷7 N下磨损率可减少到4.7×10-4 mm3/m.