Tribological behaviour of HVOF sprayed near-nanostructured and microstructured WC-17wt.%Co coatings

A ‘duplex cobalt coated’ near-nanostructured WC-17wt.%Co powder was used to produce nanostructured coatings. The tribological performance of this coating was compared with a commercial WC-17wt.%Co microstructured coating using a pin-on-plate method (ASTM G133-05 standard) with a data acquisition software to perform a real time analysis of the sliding wear process. The wear rate was studied using loads from 10 to 60 N and for various sliding distances. The metallurgical analysis of the coatings showed that the duplex Co coated powder could be sprayed to produce dense coating. Furthermore, the near-nanostructured coating showed better fracture toughness values and this corresponded to a difference in wear mechanism between the two types of coatings. The greater “plasticity” in the near-nanostructured coating was recorded as microgrooves in the wear tracks and, in comparison, brittle fracture was observed in the wear tracks produced on the microstructured coating.     

Cf/SiC表面等离子喷涂金属过渡层及其界面结合特征

目的采用等离子喷涂工艺(APS)在C_f/SiC复合材料表面制备金属涂层。方法在对比等离子喷涂Mo粉、NiCrBSi粉以及自制的Ti70Ni20Cu10复合粉末三种涂层的组织形貌和界面结合的基础上,制备了Mo-10%Ti复合涂层,喷涂用粉为通过低速球磨方法在大颗粒的Mo粉表面包覆TiH_2粉末而得,喷涂时将基体预热至700℃,在氩气保护气氛下进行喷涂。结果 APS制备的Mo-10Ti涂层,组织致密均匀,孔隙率较低,无明显裂纹。涂层与基体结合紧密,没有发生剥离现象,结合强度超过6.3 MPa,断裂发生于基体侧。结论材料的热膨胀系数和润湿性是影响等离子喷涂金属涂层与C_f/SiC复合材料结合的关键因素,所设计的Mo-Ti复合涂层较好地兼顾了这两点。     

超超临界机组耐热钢高温短时持久性能影响因素研究

某超超临界机组叶片使用的12％Cr系耐热钢调质处理后,常温力学性能及金相组织满足规范要求,但高温短时持久性能出现明显的分散性.为提高和稳定材料的高温持久性能,对典型的同炉次持久试样进行试验分析,以研究短时持久性能差异的影响因素.研究表明:材料短时持久断裂属于典型的蠕变断裂方式,短时持久强度下降与持久试验温度下板条间和晶界的碳化物粗化有密切关系,能谱分析进一步发现孔洞处脱落物B元素含量较高,达到19.98％,说明晶界的B在高温持久过程中开始向晶内迁移并形成含B的第二相质点,晶界强度明显削弱,在高温持久试验中会造成高温强度的迅速下降并快速断裂,断裂的位置大多是沿晶的,个别会在夹杂物或第二相造成的孔洞处萌生发展.     

复合涂层对钢结构耐蚀性的影响分析

采用低压等离子喷涂方法,制备了Q345A钢结构的单一Al涂层和Al-25％Cr-5％纳米SiO2复合涂层,并进行了人造酸雨全浸腐蚀和中性盐雾腐蚀的测试和分析.结果表明:低压等离子喷涂Al-25％Cr-5％纳米SiO2复合涂层,能显著提高钢结构的耐蚀性,且耐蚀效果较单一Al涂层好.与未经处理试样相比,喷涂了这种复合涂层的Q345A钢结构经20天人造酸雨全浸腐蚀后的质量损失率降低了91.90％,经10天中性盐雾腐蚀后的质量损失率从15.95％降至2.01％.     

Processing of Fe-6.5wt.%Si alloy foils by cold rolling

Thin foils of 50 μm in thickness of Fe-6.5wt.%Si alloy were obtained by conventional hot-cold rolling method. The rolling texture and basic mechanical properties of the foils were examined. The foils were heavily work-hardened and exhibited high tensile fracture strength with some extent of plastic elongations. Their bending ductility was more remarkable.     

The Sn/Ni-7Wt.%V interfacial reactions

Ni-7wt.%V(8at.%V) is an important under bump metallization material, and Sn is the primary element in most solders. This study examines the Sn/Ni-8at.%V interfacial reactions at 160°C, 200°C, 250°C, 300°C, 325°C, 350°C, and 400°C. Unlike the interfacial reactions in the Sn/Ni couples, a ternary T phase and the binary Ni₃Sn₄ phase are formed at 160°C. The vanadium solubility in the Ni₃Sn₄ phase is only 0.2 at.%, while the T phase contains 13.9at.%V. Similar results are found in the couples at 200°C, and the reaction paths are Sn/Ni₃Sn₄/T/Ni-V. The reaction paths are liquid/T/Ni₃Sn₄/Ni-V at 250°C and 300°C and are liquid/Ni₃Sn₄/Ni-V at 350°C and 400°C. Because the reaction products and the reaction rates in the Sn/Ni-8at.%V and Sn/Ni couples are different, reliabilities of the electronic products with the Ni-8at.%V barrier layer should not be assessed based only on the results of the Sn/Ni couples.     

Solid state and liquid phase sintering of mechanically activated W–20 wt.% Cu powder mixture

W–20 wt.% Cu powder mixture was mechanically alloyed by high-energy ball milling for various times and the effect of mechanical alloying (MA) on the sintering response of the composite compacts was investigated. The densification, microstructure, hardness and electrical conductivity after solid phase sintering (SPS) and liquid phase sintering (LPS) were examined. It was shown that the microstructure of mechanically alloyed powder profoundly influence the sintering response, i.e. a meaningful relationship between the sintering kinetics and the milling time was observed. It is suggested that MA disintegrates the W–W particle networks and increases the contribution of solid phase sintering (SPS) of nanostructured Cu and W particles on the densification. Higher hardness and conductivity were achieved by prolonged MA and SPS, indicating a lower W–W contiguity of the milled powders compared with the conventionally prepared W–Cu composite. On the other hand, depression of the melting temperature of copper up to 145 °C was noticed by affording a prolonged MA. The lower melting temperature and finer distribution of the Cu particles in the W matrix enhanced the densification during LPS and improved the homogeneity and properties of the final product.     

定向凝固Fe-6.5wt%Si合金热压缩变形行为研究

采用Gleeble 1500热模拟机对定向凝固Fe-6.5%(质量分数)Si合金进行热压缩变形研究。结果表明,Fe-6.5%(质量分数)Si合金柱状晶组织热形变过程中很难发生动态再结晶,以动态回复为主,易产生严重的变形带;在无序相区间,在柱状晶晶界处发生动态再结晶形核,但长大受到限制,仅局限于晶界附近。与锻态等轴晶组织相比,有序相区间,两种组织形变行为基本一致,受温度影响剧烈,在无序相区间,随温度升高,等轴晶组织的形变激活能略有升高,平均值约为294kJ/mol,而柱状晶组织的形变激活能逐渐降低,平均值约为260kJ/mol。     

Effects of γ-irradiation and Deformation Temperature on Tensile Properties of Pb-2 mass% Sb Alloy

Effects ofγ-irradiation and deformation temperature(T)on the tensile properties of Pb-2mass% Sb alloys were studied.The samples were annealed at 458 Kfor 2hin air,then water quenched after they wereγ-irradiated(the different doses were 0.5,1.0,1.5,and 2.0 MGy).The tensile properties were performed using stress-strain measurements at a constant strain rate(1.2×10~(-3) s~(-1))and at different T(303-393K).It was found that at constant dose,the fracture stress(σF)decreases while the fracture strain(εF)increases as Tincreases.At particular T,σFincreases whileεFdecreases with increasing dose.The strain-hardening exponent(n),which is the slope of the relation between ln(σ)and ln(ε)of the parabolic part of the stress-strain curve,was determined and its values increase as Tincreases and decrease as the dose increases.The value of the activation energy increases as the dose increases from 0.07 eV for un-irradiated sample to 0.1eV for the 2 MGy-irradiated sample.These values are in accordance with that needed for dislocation movement and ordering process.An interpretation of the results was given,based on the creation of point and line defects due toγ-irradiation,and that results in a distribution of beta phase(Sb-phase),leading to a difficulty in the movement of dislocations,so there is an increase in alloy hardness.     

Al-5％Pb合金的超声波分散效果

以A1-5％Pb合金为对象，研究了超声波工艺参数对Pb溶质分布的影响。利用背散射电子成像（BSE）扫描对试样进行了检测，测试了试样的硬度及磨损性能。实验结果表明：在铸造条件下，采用超声波处理能够有效抑制Al-Pb合金的溶质偏析。超声波功率对Pb溶质分散性有直接的影响，功率过大或功率过小都达不到令人满意的分散效果；过短的处理时间达不到Pb溶质分散的目的，而过长的处理时间会使Pb粒子发生聚集，只有采用合适的处理时间才能达到理想的分散效果。Pb溶质分散得细小均匀可以有效地提高硬度及耐磨性。