Microstructures and properties of nickel-titanium carbide composites fabricated by laser cladding

In this work, Ni/TiC composites were synthesized by the laser cladding technique (LCT). A scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness meter, electrochemical workstation, and friction and wear tester examined the microstructure, surface morphology, phase structure, microhardness, wear, and corrosion resistances of the Ni/TiC composites. These results indicated the Ni/40TiC composite contained finer equiaxed crystals than the Ni and Ni/20TiC composites. In addition, numerous TiC particles in the Ni/40TiC composite impeded growth of the nickel crystals, which resulted in the fine microstructure of the Ni/40TiC composite. The Ni, Ni/20TiC, and Ni/40TiC composites exhibited face-centered cubic (f c c) lattices. The average microhardness values of the Ni/20TiC and Ni/40TiC composites were approximately 748 HV and 851 HV, respectively. The Ni/40TiC composite had the lowest friction coefficient (0.43) among all three coatings, and only some shallow scratches appeared on the surface of the Ni/40TiC composite. The corrosion potential (E) of Ni/40TiC exceeded the Ni/20TiC composite, and both were larger than the Ni composite, which indicated the Ni/40TiC composite had outstanding corrosion resistance and the Ni composite had poor corrosion resistance. The corrosion current densities (i) of Ni, Ni/20TiC, and Ni/40TiC composites were 5.912, 4.405, and 3.248 μA/cm², respectively.     

Ni对铁基合金粉块氩弧堆焊层组织和性能的影响

通过氩弧焊在基体材料Q235钢板上熔敷铁合金混合粉末压块,研究了压块成分及堆焊工艺对堆焊层组织及性能的影响。结果表明:在固定压块粉末总质量为16 g、镍铁含量为0.64 g、堆焊电流为180 A时,堆焊层的硬度最大,达到HRC48.9;耐磨性最高,相对磨损量为0.013 4 g/(cm^2·min)。     

双相不锈钢表面激光熔覆钴基合金组织和性能研究

目的提高2205双相不锈钢的耐磨性和耐腐蚀性能。方法采用激光熔覆技术,在2205双相不锈钢基体表面制备钴基合金熔覆层。用X射线衍射仪、光学显微镜检测钴基合金熔覆层的相组成和显微组织,用能谱仪测定熔覆层和基体界面区域的Fe和Cr元素分布,确定熔覆层界面过渡区域的宽度。用显微硬度计和湿砂磨粒磨损试验机,测试熔覆层硬度和耐磨性能。采用扫描电镜观察摩擦表面的磨损特性,分析钴基合金熔覆层的磨损机理。用电化学工作站测试熔覆层的电化学腐蚀特性,并用2205双相不锈钢作为对比试样做相应的性能试验。结果熔覆层由γ-Co固溶体和少量的Cr7C3、Cr2Ni3化合物相组成,界面处的熔覆层相组织是少量的平面晶和胞状晶,其他区域是发达的树枝晶。由于熔覆层由多道搭接和多层熔覆形成,树枝晶生长有方向性,但不是成固定的方向,并出现明显的分层现象。熔覆层过渡区范围为50μm左右,熔覆层平均显微硬度达477HV(0.1),远高于2205双相不锈钢基体(265HV(0.1))。当磨程达到3354m时,熔覆层的质量损失仅为10.3 mg,约为基体质量损失的1/3。在3.5%NaCl溶液中,熔覆层具有较高的极化电阻与电荷转移电阻和较小的自腐蚀电流。结论熔覆层组织致密,无气孔、裂纹等缺陷,与基体呈良好的冶金结合,钴基合金熔覆层具有良好的耐磨粒磨损性能和耐腐蚀性能。     

激光熔覆SiO2/La2O3梯度生物陶瓷涂层生物活性研究

目的研究SiO_2含量对钛合金表面激光熔覆梯度生物陶瓷涂层生物活性的影响。方法利用激光熔覆技术,采用梯度成分设计思想,固定涂层中稀土氧化物La_2O_3的添加量,在钛合金TC4表面制备了掺杂不同含量SiO_2的梯度生物陶瓷涂层。采用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、噻唑蓝(MTT)及荧光素双醋酸酯(FDA)染色等测试手段,研究了SiO_2含量对激光熔覆制备梯度涂层的组织结构和生物活性的影响。结果 SiO_2在激光熔覆过程中可以降低梯度生物陶瓷涂层的开裂敏感性,并起到细化晶粒的作用。当SiO_2掺杂量为2.5%时,激光熔覆过程中诱导合成的HA+CaTiO_3数量最大;当SiO_2掺杂量为7.5%时,模拟体液(SBF)实验表明,涂层的矿化沉积能力最强。MTT测试表明,SiO_2掺杂量为7.5%的涂层细胞增殖数量的OD值最大,细胞能够紧贴涂层表面生长。FDA染色分析表明,SiO_2掺杂量为7.5%的涂层上细胞数量最多,且分布均匀。结论 SiO_2掺杂量深刻影响着生物活性陶瓷相HA和Ca_2SiO_4数量,进而影响生物陶瓷涂层的生物活性。SiO_2掺杂量为7.5%的涂层具有最佳的生物相容性及生物活性。     

Mg-Gd-Y-Zr合金TIG电弧熔覆层微观组织演变及力学性能研究

目的 在AZ91D镁合金表面熔覆Mg-Gd-Y-Zr合金，分析熔覆层微观组织演变规律及其对熔覆层力学性能的影响。方法 采用直流脉冲钨极氩弧焊（DC PTIG welding），在不同平均电流下，将Mg-Gd-Y-Zr合金焊丝送入AZ91D镁合金熔池，制备熔覆层。采用金相显微镜、扫描电子显微镜、能谱仪及X射线衍射仪，分析不同平均电流条件下的熔覆层微观组织。基于显微维氏硬度仪与往复式滑动摩擦磨损设备，表征熔覆层硬度及摩擦学性能。结果 熔覆层微观组织主要由α-Mg、Mg24(Gd,Y)5及Al2(Gd,Y)相组成。熔覆层呈现明显分层特征，主要是由晶界Mg24(Gd,Y)5相分布差异造成。平均电流增大，熔覆层中心晶粒尺寸先保持不变，而后快速增大，Al2(Gd,Y)相由细小弥散颗粒变为团聚状分布，晶界Mg24(Gd,Y)5相则由连续网状演变为不连续岛状，直至变为细小颗粒状。熔覆层硬度随平均电流增加，呈现略微上升，随后快速下降的趋势，其最高硬度达90.8HV。摩擦磨损测试过程中，平均电流为110 A所得熔覆层失重速率小于AZ91D基材。结论 采用DC PTIG在AZ91D基体表面成功制备了耐磨性能优于基体的含Gd、Y稀土元素的熔覆层，稀释率决定熔覆层Al2(Gd,Y)相形貌及分布规律。     

Microstructure and properties of WC-12Co composite coatings prepared by laser cladding

A comprehensive study of the phase composition, microstructure evolution, microhardness and wear performance of WC-12Co composite coatings fabricated by laser cladding using coaxial powder-feed mode was presented. It was shown that a combination of high scan speed and high laser energy density made WC on the edge of WC-12Co composite powders partially melt in liquid Co and 304 stainless steel matrix, and then new carbides consisting of lamellar WC and herringbone M₃W₃C (M=Fe, Co) were formed. Meanwhile, WC-12Co composite coatings with no porosity, cracks and drawbacks like decarburization were obtained, showing high densification and good metallurgical bonding with the substrate. Furthermore, a considerably high microhardness of HV_0.3 1500-1600, low coefficient of friction of 0.55 and wear rate of (2.15±0.31)×10^-7 mm³/(N·m) were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of composite coating under laser power of 1500 W.     

Al2O3 eliminating defects in the Al coating by laser cladding to improve corrosion and wear resistance of Mg alloy

Although Al produces a solid metallurgical bonding with Mg alloy substrates, micropores or crevices in the Al coating can reduce the resistance of Mg alloy to corrosion. In this study, a composite coating with a defect-free microstructure was prepared on the AZ31 Mg alloy substrate by introducing Al₂O₃ into the Al matrix via the method of laser cladding. On the one hand, Al₂O₃ with thermal insulation had a low thermal expansion coefficient and was not very prone to voids during laser melting. On the other hand, Al₂O₃ particles with a small size acted as the filler in the micropores or crevices. The Al/Al₂O₃ coating exhibited a smaller current density (2.1 × 10⁻⁶ A/cm²) in comparison with those of bare substrate and Al coating (158.4 × 10⁻⁶ and 3.1 × 10⁻⁶ A/cm², respectively), which was mainly ascribed to the pore-free microstructure and high resistance to corrosion of Al₂O₃ phase. A favorable microhardness value of 95.3 HV was achieved for Al/Al₂O₃ coating, approximately 1.8 times higher than that of Al coating (52.8 V), which was mainly ascribed to the dispersion hardening of Al₂O₃ phase. Meanwhile, the Al/Al₂O₃ coating significantly reduced wear volume from 2.8 mm³/m of Al coating to 0.4 mm³/m, showing great potential for weight reduction applications.     

A dense and compact laser cladding layer with solid metallurgical bonding significantly improved corrosion resistance of Mg alloy for engineering applications

Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm² for Mg alloy to 13 μA/cm² for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications.     

TiC含量对TC4合金激光熔覆层组织和性能的影响

采用激光熔覆工艺在TC4钛合金基体表面制备了添加不同质量分数(0%、2%、4%、6%)TiC的Ni60A复合熔覆层,通过光学显微镜、显微硬度计、X射线衍射仪、摩擦磨损机分析了不同TiC含量对熔覆层组织及性能的影响。结果表明:未添加TiC的熔覆层组织以树枝晶为主,添加TiC后出现了花瓣状物相;XRD分析发现熔覆层中出现了AlCCr₂、Al_0.24B_0.01Ni_0.75等硬质增强相,这些能够显著提高熔覆层的硬度。显微硬度及摩擦磨损试验结果表明,添加TiC的熔覆层平均硬度均较基体硬度有大幅提高,摩擦因数显著降低,且随TiC含量的增加,熔覆层硬度先增加后降低,摩擦因数先降低后增加,4%TiC熔覆层的硬度最大,相比基体提高了213.3%,摩擦因数最小,为0.309 774。     

上水口环形吹氩对中间包内渣眼形成的影响

 中间包上水口环形吹氩可以在塞棒周围形成清洗钢液的环形气幕，同时部分氩气泡随钢液进入上水口内，可以减少非金属夹杂物在水口内壁的黏附，起到防止水口堵塞的作用。然而，不合理的吹氩量会导致中间包内液面渣层受过强的气液羽流冲击而形成渣眼，使得钢液裸露并发生二次氧化，严重影响铸坯质量。采用标准 k ε 湍流模型研究中间包内流体流动，采用DPM模型和VOF模型耦合方法，研究上水口环形吹氩条件下渣眼的形成及演化规律。结果表明，上水口环形吹氩在塞棒周围形成较强的上升流，塞棒上部邻近区域存在多个涡流区；在钢液涡流的影响下，中间包液渣下层远离塞棒区域，上层向塞棒区域迁移；随着吹氩量的增大，平均湍动能增大，塞棒附近钢液速度逐渐增大，钢渣界面钢液速度先增大后减小，渣眼边缘钢液速度先增大后减小然后再增大，速度与垂直方向夹角逐渐减小；增大吹氩量，中间包熔池液面形成以塞棒为中心的渣眼，渣眼面积逐渐增大。试验条件下不产生渣眼的临界吹氩量为4.2 L/min，对应的钢渣界面最大速度为0.247 m/s，与垂直方向夹角为70°。