On the evaluation of adhesion of coatings by automatic scratch testing

Automatic scratch testing is an expedient technique for comparatively evaluating the cohesive failure load and adhesion failure load of thin coatings on various substrates. In combination with SEM examination of the scratch track, this technique has been used herein to detect and evaluate various effects on coating strength and adhesion. For soft Triballoy T-800 and Stellite SF-6 cobalt-base coatings on 4340 low alloy steel, adhesion was found to be strong and failure was found to be cohesive in the coating. In the presence of a plated chromium interlayer, pre-existing cracks lowered substantially the cohesive failure load, which was also lowered by an increase in the coating deposition pressure. The spacing of transverse cracks within the coating was found in all cases to decrease with increasing applied normal load. In soft aluminum coatings on depleted uranium (DU)-0.75% Ti alloy specimens, alloying aluminum with magnesium or zinc enhanced the coating strength and adhesion. In (Al-Mg) coatings on this substrate, a smoother surface led to a lower friction coefficient and a higher adhesion failure load. In hard, thin TiN coatings on 17-4 PH steel, a lower bias voltage applied to the substrate yielded higher cohesive and adhesion failure loads. In hydrogenated amorphous SiC thin coatings on 4340 steel, loss of hydrogen by annealing converted the residual compressive stresses into tensile stresses and lowered both the cohesive and the adhesion failure loads. Finally, automatic scratch testing proved helpful in determining delamination loads in multilayer TiN/Ti/TiN coatings on DU-0.75% Ti alloy.     

Microstructure,adhesion, and tribological properties of conventional plasma-sprayed coatings on steel substrate

A variety of metallic and oxide coatings were deposited under various conditions on 1020 mild steel substrate by conventional plasma spraying. The coating thickness, microhardness, cohesion and adhesion failure loads, friction coefficient, and abrasive wear resistance were evaluated. The coatings were classified as follows, in order of decreasing microhardness and wear resistance: alumina, chromia, 316 stainless steel, Ni-5% Al, elemental aluminum and aluminum-polyester. Wear resistance increased with increasing microhardness and decreasing friction coefficient. The microhardness and wear resistance of high-velocity oxy-fuel (HVOF) diamond jet (DJ)-sprayed aluminum were found to be superior to those of plasma-sprayed aluminum. Plasma or flame-sprayed metallic coatings adhered well to the substrate. The cohesion, adhesion, microhardness, and wear resistance of alumina coatings exceeded those of equally thick chromia coatings.     

Deposition and mechanical property evaluation of amorphous silicon-containing diamond-like carbon (Si-DLC) coatings on steel

Amorphous silicon-containing diamond-like carbon (Si-DLC) coatings were deposited by Ar⁺ ion beam-assisted physical vapor deposition of tetraphenyl-tetramethyl-trisiloxane (704 Dow Corning diffusion pump oil). The steel substrates studied included AISI 4130, 17-7 PH, 440-C, and 4340 (bare and nitride-precoated) specimens. DLC coating thicknesses ranged from 1.8 to 4.31 μm. Deposition rates increased with increasing beam current density and varied with the steel substrate composition. Nanoindentation measurements of the hardness and elastic modulus at two different depths yielded values of 9-10 GPa and 99-128 GPa, respectively. Film cohesion and adhesion failure loads increased with increasing underlying layer hardness, chromium content in the substrate, or the presence of a titanium nitride precoat. The friction coefficient of a diamond stylus against the coating surface decreased and wear resistance increased with nitride precoating.     

Effects of adhesive fillers on the strength of tubular single lap adhesive joints

When an adhesively bonded joint is exposed to a high environmental temperature, the tensile load capability of the adhesively bonded joint decreases because the elastic modulus and failure strength of the adhesive decrease. In this paper, the elastic modulus and failure strength of the adhesive as well as the tensile load capability of the tubular single lap adhesively bonded joint were experimentally and theoretically investigated with respect to the volume fraction of filler and the environmental temperature. Two types of fillers - Al₂O₃ (alumina) and chopped fiber E glass - were used. From the experiment, it was found that the elastic modulus and failure strength of the adhesive increased in accordance with the increase of volume fraction of the filler and decreased with the environmental temperature rise. It was also found that the tensile load capability of the tubular single lap adhesively bonded joint decreased as the environmental temperature increased; however, it had no correlation with the volume fraction of filler because of the effect of the fabrication thermal residual stresses generated by the CTE difference between the adherend and adhesive.     

粉煤灰对混凝土表层渗透性能的影响

把不同粉煤灰掺量的混凝土试件浸泡在超纯水中,通过表面渗透测试仪定期检测混凝土试件的表层渗水系数,研究粉煤灰对混凝土表层渗透性能的影响.结果发现:掺入粉煤灰量的大小对表层渗水性能的影响较大,标准养护28 d后,掺入比例为15％的粉煤灰混凝土和普通混凝土相比,表层渗水系数减小,当粉煤灰量达到30％时,表层渗水系数与普通混凝土几乎相等;随着浸泡龄期的增长,混凝土表层渗水系数不断减小;浸泡150 d后,两种粉煤灰掺量混凝土的表层渗水系数仅为普通混凝土试件的40％左右.     

聚丙烯纤维对混凝土耐硫酸盐腐蚀性能的影响

采用一种新的混凝土耐硫酸盐腐蚀试验方法,通过测试混凝土质量腐蚀系数、抗压强度腐蚀系数和抗拉强度腐蚀系数,研究掺加不同种类聚丙烯纤维的纤维混凝土耐硫酸盐腐蚀性能.研究结果表明,相同配比纤维混凝土抵抗(NH4)2SO4溶液侵蚀能力远远低于Na2SO4溶液,而纤维的掺入明显改善了混凝土的耐硫酸盐腐蚀能力;单掺聚丙烯细纤维的混凝土质量损失最少;混掺聚丙烯网状纤维和钢纤维的混凝土抗压强度损失最少;混掺聚丙烯粗纤维和钢纤维的混凝土抗拉强度损失最少.     

三分螺旋折流板换热器内二次流分布与强化传热关系分析

通过对倾斜角35°首尾相连的三分螺旋折流板换热器的数值模拟,展示了其壳侧通道内流体在典型切面上的流场和流线分布,以及典型切面上典型直线的流动和换热参数分布,并与性能测试结果进行了对比。结果表明,数值模拟结果与实验结果是吻合的。螺旋折流板形成的近似螺旋通道,使换热器壳侧流体受离心力和向心力共同作用形成了迪恩涡二次流,且在每个螺旋周期内都存在;二次流增强了主流区域流体与靠近壁面流体的掺混,使得壳侧典型切面上中心线和折流板外缘直线的轴向速度较大;除主流中心区域外,壳侧流体在二次流的作用下具有均匀的湍流动能;二次流所在区域内,壳侧同心柱面内典型直线上换热系数相差不大,但由于二次流能使其附近区域传热面上的流体得到不断卷吸掺混,由此强化传热。     

聚合物粉体动摩擦因数的影响实验研究

设计了一套自动化实验数据采集程序,实现了对于压力、扭矩和温度的多参数、在线数据采集,并基于LabVIEW数学函数功能计算出粉体物料动摩擦因数。研究了在不同压力、温度、转速和材料种类时,其动摩擦因数的变化情况,并分析不同压力、温度、转速和材料种类等因素对动摩擦因数的影响。结果表明,动摩擦因数随着压力的增大而降低,且压力、温度和转速这些因素是相互影响的;不同粉体材料的性质对动摩擦因数有着很大影响,其中聚四氟乙烯粉体动摩擦因数最低,并且橡胶粉体动摩擦因数随着颗粒的增大而增大;动摩擦因数测试结果证明所设计的测试系统是切实可行的,而且数值的准确度和精度都比较高。     

Diffusion coefficient of carbon in Fe–Ni alloy during synthesis of diamond under high temperature and high pressure

Synthetic diamond particles were prepared under high temperature and high pressure using arrayed seeds. A dense Fe–Ni alloy shell covered each diamond seed during synthesis; the growth of diamond particles was controlled by the diffusion of carbon through the metallic shell. The diffusion coefficient of carbon through Fe–Ni melt at 1600 K and 5.5 GPa is about 5×10^?6 cm²/s, with an activation energy for diffusion of 336 kJ/mol.     

玻璃微珠改性热塑性聚酰亚胺研究

采用玻璃微珠改性热塑性聚酰亚胺（PI—T）,考察了玻璃微珠粒径和用量对PI—T力学性能的影响,并用热机械分析仪（TMA）测定了改性PI—T的线胀系数。结果表明,改性PI—T的弯曲和拉伸弹性模量显著提高;线胀系数随玻璃微珠质量分数的增加呈降低趋势;玻璃微珠和PI—T基体的结合较差;改性PI—T的拉伸强度和冲击强度都有不同程度的降低;小粒径（5μm）较大粒径（20μm）玻璃微珠改性PI—T的冲击强度降低缓慢。