NiCrAl/NiCg 封严涂层高速可磨耗性能研究

NiCrAl/NiCg 可磨耗封严涂层可以提高涡轮发动机效率, 已广泛应用于航空发动机中高压压气机部位。 本 文采用高温高速刮擦试验方法对 NiCrAl/NiCg 封严涂层进行模拟服役工况条件下的可磨耗试验, 试验后通过对磨 损表面宏观形貌、 微观组织形貌、 磨损质量以及叶片高度磨损比等数据进行分析以评价涂层的可磨耗性能。 结果 表明, NiCrAl/NiCg 封严涂层在不同的试验条件下均表现出优异的可磨耗性能, 可以保护叶片免受损伤; 当进给 速率由 5 μm/s 提高到 500 μm/s 时, 叶片涂层质量磨损比 (IQR) 值、 叶片高度磨损比 (IDR) 均显著提高, NiCrAl/ NiCg 封严涂层的可磨耗性有所下降; 单次刮削深度是影响 NiCrAl/NiCg 封严涂层可磨耗性能的重要影响因素, 单次刮削深度越小, NiCrAl/NiCg 封严涂层的可磨耗性能越优异。 该研究为航空发动机应用中叶尖与可磨耗封严 涂层相互作用的探索提供了新的基础数据, 也为今后封严涂层性能研究及选定提供参考依据。     

Cu－Zn－Al形状记忆弹簧的热循环特性

本文研究了Ｃｕ－Ｚｎ－Ａｌ形状记忆弹簧在外加应力不同热循环方式下的性能变化规律，试验分别测试了弹簧的低温残余应变和高温残余应变，结果表明：在外加应力的热循环过程中，影响双程记忆性能的主要因素是高温残余应变，不完全相变热循环时记忆性能衰减缓慢。     

金属加工设备防腐防护外涂层的应用现状研究

防腐防护外涂层,是防止金属加工设备内腐蚀的关键措施.从环氧、聚酯类、防静电、纳米复合等防腐防护外涂层,研究其应用现状,并对以上防腐防护外涂层做出性能评价.     

FeSiAl电磁屏蔽涂层的腐蚀行为对吸波性能的影响

以在Q235冷轧钢板表面涂敷的FeSiAl电磁屏蔽涂层为研究对象，通过改变固化条件，探究了电磁屏蔽涂层的最优固化环境.同时，运用中性盐雾试验、电磁屏蔽性能测试和电化学阻抗试验，研究了自然条件固化后涂层的吸波性能和耐蚀性能随盐雾周期不同的变化规律.结果表明，电磁场下固化会损害涂层的腐蚀屏蔽性.吸波剂含量的增加不利于提升涂层的吸波性能，同时也会损害涂层的腐蚀屏蔽性.长期盐雾试验后，涂层的吸波性能随腐蚀屏蔽性的降低而下降.      

老化方式对聚氨酯涂层钢板失效行为的影响

运用四种加速方法对聚氨酯有机涂层钢板进行老化,并通过涂层的表观性能和电化学特征对比研究了老化方式对涂层失效的影响.紫外老化对涂层光泽的影响最大,老化32 d失光度达85.7%.盐雾实验前期线性极化阻力R_p迅速下降,后期由于盐膜的生成使得R_p保持稳定;氙灯和盐雾混合老化的光泽度和R_p的变化规律都表现为实验前期与光老化相似,后期则与盐雾实验相类似.此外,拟合不同老化方式的电化学交流阻抗谱发现:混合老化前期主要受氙灯影响,与单一氙灯老化的等效电路一致,表现为两个时间常数;后期产生盐膜,出现三个时间常数.      

外加拉应力对13Cr马氏体不锈钢的腐蚀行为影响

采用电化学测试手段(开路电位、交流阻抗谱及动电位极化曲线测试), 结合接触角测试及体视显微镜微观形貌观察探究在80 g·L-1 NaCl溶液中拉应力对L80-13Cr马氏体不锈钢钝化膜溶解与再修复机制的影响.结果表明, 拉应力大小与L80-13Cr的钝化特性存在正相关关系.随着外加拉应力的增大, L80-13Cr马氏体不锈钢的开路电位负移, 电子转移电阻减小, 线性极化电阻减小, 反应速率随着拉应力的增大而增大.而L80-13Cr马氏体不锈钢在高电位下再钝化形成的钝化区会缩短, 自腐蚀电位降低, 维钝电流密度增加.接触角测试和体视显微镜微观形貌观察发现, 拉应力使得表面接触角减小, 不锈钢表面容易发生点蚀.外加拉应力使得L80-13Cr马氏体不锈钢的表面能增加, 促进钝化膜的溶解, 并且抑制钝化膜的再生, 导致材料耐蚀性降低.      

氨基硅烷化对AZ31B镁合金阴极电泳涂层性能的影响

采用阴极电泳技术在镁合金表面沉积防腐保护涂层,研究了KH460水溶性氨基硅烷预处理对阴极电泳涂层与基体镁合金的结合力及耐腐蚀性能的影响。采用SEM观察了镁合金表面硅烷膜层形貌,并通过极化曲线测试评价了膜层耐腐蚀性能。采用NMP测试及电化学交流阻抗分别评价了电泳涂层的抗溶胀能力及耐腐蚀性能。结果表明,硅烷膜层在镁合金表面非常薄呈透明状,且具有一定的防护性能。经硅烷预处理后可以大大提高镁合金阴极电泳涂层的结合力,NMP溶液浸泡170 h后涂层依然完整;无硅烷预处理试样则浸泡14 min之后,涂层完全脱落。此外,硅烷预处理也可极大地改善电泳涂层阻抗性能,涂层在5%NaC l溶液浸泡616 h后,低频阻抗值高达1×109Ω,比未预处理试样的阻抗高3个数量级,涂层仍然具有良好的阻挡腐蚀电解液渗透的能力,耐腐蚀性能优异。     

Cu-Cr-Zr合金热变形行为

在Gleeble-1500D热模拟试验机上,采用高温等温压缩试验,在变形温度650~850℃、应变速率0.001~10 s~(-1)和总压缩应变量50%的条件下,对Cu-Cr-Zr合金的流变应力行为进行研究.通过应力-应变曲线和显微组织图分析了合金在不同应变速率、不同应变温度下的变化规律.结果表明:应变速率和变形温度对合金再结晶影响较大,变形温度越高,合金越容易发生动态再结晶;应变速率越小,合金也同样容易发生动态再结晶,并且对应的峰值应力也越小.从流变应力、应变速率和温度的相关性,得出了该合金热压缩变形时的热变形激活能Q和流变应力方程.研究分析Cu-Cr-Zr合金的热加工性能,可为生产实践提供理论指导与借鉴.     

ZM5镁合金超音速微粒沉积Al-Si涂层的耐腐蚀性能

为提高镁合金的耐蚀性能,采用超音速微粒沉积技术在ZM5基体上制备Al-Si防护涂层。采用环氧面漆对涂层进行封孔处理,采用电化学方法和中性盐雾实验对镁合金基体、涂层及涂层封孔后的抗腐蚀性能进行测试。结果表明:防护涂层致密,缺陷少,可显著提高ZM5镁合金的耐蚀性能;腐蚀电流密度比基体降低2~3个数量级,阻抗模值提高2个数量级,而涂层封孔后耐蚀性能进一步提高。相比镁合金24 h严重腐蚀,涂层中性盐雾实验1 000 h仅轻微腐蚀,腐蚀造成的质量损耗较小,封孔后涂层未见明显腐蚀,可为镁合金提供长效防护。     

AC-HVAF 喷涂微纳米复合 WC 涂层 在水电设备抗空蚀工程中的应用

水轮机过流部件的空蚀损伤引起设备本体材料流失, 破坏机组结构, 降低机组运行安全性。 涂层防护是抗 空蚀损伤的主要手段, 本文拟通过降低涂层孔隙率提高涂层的抗空蚀性能。 采用空气助燃超音速火焰喷涂技术 (AC-HVAF) 制备了微纳米复合 WC 涂层, 分别采用静态振动空蚀试验和高速流体空蚀试验进行涂层抗空蚀性能 表征, 结果表明, AC-HVAF 喷涂的微纳米复合 WC 涂层孔隙率为 0.2%, 涂层孔隙细小, 分布均匀, 涂层抗空蚀 性能优于传统 HVOF 喷涂涂层。 在水电站现场应用结果表明, 经过 5.5 年运行后, 涂层完好。 AC-HVAF 喷涂微 纳米复合 WC 涂层可有效提高水电设备的抗空蚀能力, 提高了机组的安全性。     

Effect of prestrain and baking on the secondary deformation properties of cold-rolled ultra-high-strength steel sheets

Two experimental steels with tensile strength above 980 MPa were prepared to investigate the effect of prestrain and baking on their mechanical and fracture behaviors. The experimental results reveal that,for both experimental steels,with increases in the prestrain level,the bake hardening value increases before reaching a maximum point,and then decreases with further increases in the prestrain level. The results of a "bending-baking-secondary bending"test indicate that the secondary bendability deteriorates at a high level of prestrain. The yield strength of the experimental steels was found to increase and the elongation to decrease after high levels of prestrain and bake hardening. Fracture morphology images indicate that a high prestrain level is associated with shallow dimples and more and larger local cleavage areas.     

The influence of strain path on subsequent mechanical properties—Orthogonal tensile paths

Several aluminum alloys have been subjected to two stage tensile straining, an initial prestrain followed by a subsequent tensile strain at 90 deg to the initial direction. In AA1100-0 and AA3003-0 the prestrain produces dislocation tangling and diffuse cell walls resulting in an enhanced flow stress and decrease in ductility when the material, is subsequently strained in the orthogonal direction. In a fine grained experimental Al−Fe−Ni alloy the prestrain is accompanied by a very low accumulation of dislocations and in this case the flow stress is reduced and ductility enhanced in subsequent orthogonal straining. The commercial alloys AA2036-T4 and AA5182-0 are unaffected by the two stage tensile strain path. The results are considered in terms of the forming limit curve and it is also shown that the behavior is consistent with the concept of an “alien” dislocation distribution being generated during the prestrain.     

Microscopic Response of TRIP Steels to Prestrain During Plastic Deformation

In order to uncover the mechanism of elastic modulus degradation during plastic deformation, uniaxial tensile test of transformation-induced plasticity (TRIP) steels under different prestrain levels was carried out. The real elastic modulus unloaded at each prestrain was calculated by linearly fitting. The microstructure evolution with plastic strain and the fracture morphology were monitored by using a scanning electron microscope (SEM). Dislocation density and its distribution were detected under a transmission electron microscope (TEM). Microscopic mechanism of the elastic modulus degradation of TRIP steels was discussed in detail. Experimental results indicated that the investigated TRIP600 steel was of severe elastic modulus degradation during plastic deformation. The new-born martensite distributed among the retained austenite, resulting in the combination of good ductility and high strength for TRIP steels. It was the change of dislocation movement that induced the variation of atomic binding force and finally led to the variation of elastic modulus.     

硬质合金金刚石涂层的残余应力分析

采用有限元方法分析硬质合金金刚石涂层的热残余应力,采用轴对称二维几何模型和自由边界条件,考虑了涂层厚度及不同基体对应力场的影响。分析表明,在多晶金刚石涂层中存在压应力,在基体中出现了拉应力,这种应力结构分布对材料性能的影响是有利的。在明锐界面出现了大的剪切应力(415MPa),应力奇异场出现在明锐界面靠近自由边界处。涂层压应力随基体中钴含量的增加而增加,随涂层厚度的增加而减小。因此可以借助这两个因素来适当控制和调节材料中的应力场以得到性能优良的产品。     

Yield behavior of a mild steel after prestraining and aging under reversed stress

Tubular specimens of mild steel are subjected to tensile prestraining and then aged under compressive stresses along the Bauschinger curve, at various temperatures below 175 °C. The compressive (reversed) stress imposed on the specimen during aging, called here the aging stress, is employed up to a maximum level of 90 pct of the prestress. Reloading tests in tension and in compression are carried out at room temperature, and the critical aging stress at which the yield stresses in the two reloading directions become equal is determined as a function of aging temperature. The critical aging stress decreases with increasing aging temperature and becomes constant at aging temperatures above 100 °C. Under such critical aging conditions, the aging index, i.e., the ratio of yield stress to prestress, rises with increasing aging temperature and approaches a saturation value of 0.86 at 150 °C. It is shown that stress aging is an effective means of reducing the Bauschinger effect while preserving the work hardening induced by the prestrain.     

Anisotropic strain localization in tensile prestrained sheet steel

Multiple forming operations are often needed to stamp complex shapes out of sheet metal. Large changes in strain path can occur from such operations. This study examined the effects of a particular strain path change, tensile-tensile, on the mechanical properties of an aluminum-killed steel. Large tensile specimens were prestrained various amounts in one direction followed by machining smaller tensile specimens at 0, 45, and/or 90 deg to the prestrain direction. The smaller samples were then pulled to failure. For samples pulled in the same direction as the prestrain, the residual strength and ductility were equivalent to those obtained from an interrupted tensile test. In contrast, both the 45 and the 90 deg prestrained specimens showed a larger than expected flow stress and an abrupt change in the nature of the residual ductility at prestrains of 7.5 pct and larger. At 7.5 pct prestrain, the uniform strain, as measured by the maximum-load point on the load vs elongation tensile curve, decreased abruptly. The decrease was accompanied by a corresponding increase in the post-uniform strain. This unusual behavior is explained in terms of a rapid increase in strain-hardening with strain.     

Near-Neutral pH Stress Corrosion Cracking Susceptibility of Plastically Prestrained X70 Steel Weldment

The application of strain-based design for pipelines requires comprehensive understanding of the postyield mechanical behavior of materials. In this article, the impact of plastic prestrain on near-neutral pH stress corrosion cracking (SCC) susceptibility of welded X70 steel was investigated with a slow strain rate tensile (SSRT) test. Generally, plastic prestrain reduces the SCC resistance in various welded zones. The SCC susceptibility of the test materials can be put in the following order: heat-affected zone (HAZ) > weld metal (WM) > base metal (BM). Fractographic analysis indicates that there are two cracking modes, mode I and mode II, during SSRT tests. Mode I cracks propagate along the direction perpendicular to the maximum tensile stress, and mode II cracks lie in planes roughly parallel to the plane where the maximum shear exists. The SCC of the BM is governed by mode I cracking and fracture of the HAZ, and the WM is dominated by mode II cracking. Damage analysis shows that the detrimental impact of plastic prestrain on the residual SCC resistance cannot be evaluated with the linear superposition model. A plastic prestrain sensitivity, a material constant independent of plastic prestrain, is proposed to characterize the susceptibility of SCC resistance to plastic prestrain, and it increases with the SCC susceptibility of the steels. The enhanced SCC susceptibility caused by plastic prestrain may be related to an increase in yield strength. The correlation of the ratio of the reduction in area in NS4 solution to that in air (RA _SCC/RA _air) with the yield strength is microstructure dependent.     

Influence of prestrain history on fracture toughness properties of steels

The effects of prestrain history on fracture toughness properties (J _Ic values andJ _R curves) of 4340 steel and 316 stainless steel were investigated. It was observed that monotonic prestrain decreased fracture toughness of both steels regardless of prestrain level. Although cyclic prestrain elevated fracture toughness of 4340 steel, it degraded that of 316 stainless steel. The effects of cyclic prestrain on fracture behavior of 4340 steel and 316 stainless steel were found to be related to cyclic softening and cyclic hardening characteristics, respectively. Moreover, material strengths rationalized the influence of prestrain history on fracture toughness properties of these two steels. Formerly with the Westinghouse Electric Corporation     

热镀锌合金化镀层裂纹产生及扩展的原位观察

用装配3点弯曲试验装置的扫描电镜原位分析了GA钢板变形情况下镀层中裂纹的产生、扩展、镀层断裂及GA钢板在塑性变形过程中镀层与钢基体界面交互作用的情况。试验及分析结果表明：镀层承受拉应力的一侧,裂纹在Г／δ,相界面处产生,在δ1相中沿着垂直于镀层平面的方向扩展,并沿着Г相／钢基体界面延伸,镀层塑性变形的迹象不明显;镀层承...     

High temperature work softening yield point phenomena in polycrystalline aluminum

Work softening yield points have been studied in high purity polycrystalline aluminum tested in the temperature rangeT ₂ = 100°to 450°C at constant strain rate subsequent to prestraining in tension at a lower temperature (T1) = room temperature or 350° C) or higher strain rate. The yield drops increase with prestrain as well as with the difference between the flow stresses at the test and prestrain temperature. Reductions in the yield drop caused by annealing atT ₂ prior to testing indicate that the yield drops are the result of dynamic recovery. It is shown that dynamic recovery is accelerated by concurrent straining.