通过凝固冷却速率调整Zn-1Mg-(0.5Mn,0.5Ca)合金的显微组织和显微硬度

生物可降解锌基合金,特别是添加合金元素的锌-镁(Zn-Mg)合金,已获得广泛研究以改善其力学性能和腐蚀性能.由于这些性能主要依赖于合金的显微组织,因此任何评价都应该从了解影响其形成的条件开始.本研究旨在探讨凝固冷却速率对Zn-1Mg-(0.5Ca,0.5Mn)(质量分数,％)合金瞬态凝固过程中显微组织演化的影响.结果表...     

Cu/Zr纳米多层膜微结构与力学性能

本文利用直流磁控溅射方法在石英玻璃基片上制备一系列自支撑Cu/Zr纳米多层膜,使用箱式电炉对多层膜进行退火处理,利用显微硬度计,X射线衍射仪、扫描探针显微镜表征了多层膜的力学性能与微观结构,研究了不同工艺参数对纳米多层膜性能的影响.研究结果表明:当Cu调制层厚从42 nm增加至140nm时,多层膜显微硬度从4.9 GPa逐渐降低至4.0 GPa;当Zr调制层厚从3.2 nm增加至4.8 nm时,显微硬度值从6.51 GPa降低至5.64 GPa,硬度值降低13.4%,而从4.8 nm增至8 nm时,显微硬度值变化不大(约5.7 GPa);合适的温度退火时,多层膜微观缺陷消失,表面形貌更均匀,显微硬度增加.利用Chu和Barnett提出的硬度增强理论模型对Cu/Zr纳米多层膜表现出的超硬现象进行了理论分析和解释.     

Effects of rare earth on microstructures and properties of Ni-W-P-CeO2-SiO2 nano-composite coatings

Ni-W-P-CeO2-SiO2 nano-composite coatings were prepared on common carbon steel surface by pulse electrodeposition of nickel, tungsten, phosphorus, rare earth (nano-CeO2) and silicon carbide (nano-SiO2) particles. The effects of nano-CeO2 concentrations in electrolyte on microstructures and properties of nano-composite coatings were studied. The samples were characterized with chemical compositions, elements distributions, microhardness and microstructures. The results indicated that when nano-CeO2 concentration was controlled at 10 g/L, the nano-composite coatings possessed higher microhardness and compact microstructures with clear outline of spherical matrix metal crystallites, fine crystallite sizes and uniform distribution of elements W, P, Ce and Si within the Ni-W-P matrix metal. Increasing the nano-CeO2 particles concentrations from 4 to 10 g/L led to refinement in grain structure and improvement of microstructures, while when increased to 14 g/L, the crystallite sizes began to increase again and there were a lot of small boss with nodulation shape appearing on the nano-composite coatings surface.     

Z3CN20-09M铸造不锈钢的热老化机理研究

为了研究Z3CN20-09M铸造不锈钢长期服役后的热老化机理,采用硬度法和透射电子显微分析法研究了国产Z3CN20-09M铸造不锈钢在400℃加速老化1×104h后的性能和组织变化.试验结果表明：与原始态相比,热老化1×104h后Z3CN20-09M钢的洛氏硬度上升了21.37%,同时由于铁素体内调幅分解形成的富Cr的α′相和富Fe的α″以及奥氏体相内的析出物导致铁素体相和奥氏体相的显微硬度分别上升了70.81%和25.15%.调幅分解所引起的铁素体脆化是材料脆性增大的主要原因.     

Zr702表面激光熔覆FeCrAl涂层微观组织及性能研究

目的 优化激光熔覆工艺参数,制备综合性能良好的FeCrAl涂层,提高Zr702基体的表面性能。方法 通过同轴送粉方式,利用激光熔覆技术在Zr702表面制备了Fe CrAl涂层,采用配备能谱仪（EDS）的扫描电镜（SEM）、X射线衍射仪（XRD）、数字显微硬度计、高速往复摩擦试验机及马弗炉研究了不同激光功率（1 300、1 400、1 600、1 800 W）与扫描速度（7、8、9 mm/s）对FeCrAl涂层成型质量、显微硬度、耐磨性及抗高温空气氧化性能的影响。结果 从所制备涂层的宏观形貌及微观组织可以观察到,在激光功率为1 600W、扫描速度为9 mm/s时,涂层成型质量最好。显微硬度测试结果表明,随着激光功率和扫描速度的增大,显微硬度呈减小趋势,但涂层显微硬度均高于Zr702基体,平均显微硬度约为基体的2.70～3.78倍。耐磨性能测试结果表明,涂层的磨损量小于Zr702基体,在激光功率为1 600 W、扫描速度为7 mm/s时,磨损量最低。氧化结果表明,800℃氧化时涂层未表现出良好的防护作用,但在1 000℃氧化时,涂层样品皆表现出优于Zr702基体的抗高温空气氧化性能。结论 ...     

铝合金表面激光熔覆铜基合金涂层研究

为了提高铝合金的表面强度,根据铜合金的液相分离性质,采用CO2激光熔覆方法,在铝合金表面成功制备了铜基合金涂层。结果表明,涂层的基体相为铜基固溶体,强化相主要为呈弥散分布的laves相。涂层中的强化相表现出了"富Mo核心"+"包围相"的复合结构特征,这主要是由于富Mo核心的析出为液相分离提供了异质形核条件所造成的。硬度测试表明,所获涂层的硬度约为270HV0.05,比ZL104铝合金提高了约2倍。     

Effect of solidification process parameters on dry sliding wear behavior of AlNiBi alloy

As-cast samples of the Al–3wt.%Ni–1wt.%Bi alloy resulting from the horizontal directional solidification process were subjected to the micro-abrasive wear test. The effects of the solidification thermal and microstructural parameters, such as the growth and cooling rates and the cellular and primary dendritic spacings (V_L and T_R; λ₁ and λ_c; respectively), were evaluated in the wear resistance of the investigated alloy. The tribological parameters analyzed were the wear volume and rate (V_w and R_w). The solidification experiments and the wear tests were carried out by means of a water-cooled horizontal directional solidification device and a rotary-fixed ball wear machine, respectively. The results show lower V_w and R_w values correspond to finer microstructures and the V_w dependence on λ₁ is characterized by an experimental mathematical equation. A better distribution of Bi soft droplets and Al₃Ni hard intermetallic particles is observed within the finer interdendritic region and, in consequence, the better wear resistance is achieved in as-cast samples with dendritic morphology rather than cellular morphology. A transition of wear mechanism from adhesive to abrasive is observed.     

Effects of doping route on microstructure and mechanical properties of W−1.0wt.%La2O3 alloys

A comparative study was conducted by using solution combustion synthesis with three different doping routes (liquid−liquid (WL10), liquid−solid (WLNO) and solid−solid (WLO)) to produce nanoscale powders and further fabricate the ultrafine-grained W−1.0wt.%La₂O₃ alloys by pressureless sintering. Compared with pure tungsten, W−1.0wt.%La₂O₃ alloys exhibit ultrafine grains and excellent mechanical properties. After sintering, the average grain size of the WLO sample is larger than that of WL10 and WLNO samples; the microhardness values of WL10 and WLNO samples are similar but larger than the value of WLO sample. The optimized La₂O₃ particles are obtained in the WL10 sample after sintering at 1500 °C with the minimum mean size by comparing with WLNO and WLO samples, which are uniformly distributed either at grain boundaries or in the grain interior with the sizes of (57±29.7) and (27±13.1) nm, respectively. This study exhibits ultrafine microstructure and outperforming mechanical properties of the W−1.0wt.%La₂O₃ alloy via the liquid−liquid doping route, as compared with conventionally-manufactured tungsten materials.     

Influence of processing parameters on microstructure and mechanical response of a high-pressure die cast aluminum alloy

Motor sealing brackets were fabricated by pressurized die casting (PDC) process under 408 MPa pressure via semisolid thick slurry of Aluminum Alloy 6061 base metal and 20% powder-chip of similar composition (average 500 μm). Initially, 81 microns powder (40% by weight) and micro-size chips (60% by weight) were mixed by stirring near 300°C until the diffusion of powder takes place and then refined by ball milling process. Influence of thick semisolid slurry modified by powder-chip reinforcement was investigated according to unmelted chip distribution inside the formed cavities, reinforcement incorporation factor (RIF), density measurement, blister formation along the surfaces and microhardness. The obtained results reveal that the unmelted particles significantly improved the microhardness value and density as 134.85 HV and 2.71 g/cm³, respectively, also with the reduction in the size of cavities. Refined microstructures were observed at several locations of the components due to the effect of processing parameters.     

Towards physical and mechanical properties of the novel Al-Cr-Ni-Fe decagonal quasicrystal and crystalline approximants

In the present article, mechanically alloyed AlCrNiFe alloy powders, including quasicrystalline and crystalline phases, were compacted through a cold isostatic pressing at 400 MPa pressure, 25 °C temperature, and 1 h soaking time. The main objective of this work is to examine the surface porosity and relative density, microhardness, compressive strength, wettability, electrical resistivity, and optical and luminescence properties of the AlCrNiFe compacts. The effect of the crystalline/quasicrystalline structures on the mentioned properties was studied. It should be noted that the physical and mechanical characteristics of the AlCrNiFe alloys were first investigated. It was diagnosed that the Vickers microhardness of the decagonal quasicrystalline compacts possesses the maximum value of 12 GPa. The AlCrNiFe compacts containing the decagonal phase acquire the maximum compressive strength and low ductility of 363 MPa and 2.53%, respectively. The highest contact angle value (θ_avg = 103.3° ± 2.3°) beside the lowest wettability and surface free energy values (W_A = 56.1 ± 2.8 mJ m^?2, SFE = 21.1 ± 1.3 mJ m^?2) belongs to the decagonal quasicrystal as compared to the PTFE. It was recognized that the presence of the decagonal quasicrystal resulted in the high electrical resistivity value of 930 μΩcm at room temperature with a negative temperature coefficient of resistivity (ρ_?253/ρ₂₇ = 1.13). Decagonal quasicrystal comprises the highest optical absorption and bandgap, which made it suitable for solar-selective absorbers.