In order to improve the service life of copper alloy propeller, four Ni45 composite coatings with 5%, 10%, 15% and 20% WC particles were prepared on the surface of copper alloy propeller by laser cladding technology. The microstructure and properties have been investigated by XRD, SEM, EDS and friction and wear tester. The results indicate that the coatings primarily consist of γ-(Fe, Ni) solid solution, Cr0.09Fe0.7Ni0.21, Ni3B2, Ni14W4 and carbides (M23C6, M7C3 and WC). The microstructure mainly consists of cellular grains, dendritic grains and hard-phase particles, which increase along with the increase in WC particles. The average values of four coatings’ microhardness are 782, 875, 1091 and 986 HV0.5, respectively. When the WC content is 15%, the average microhardness has a maximum value of 1091 HV0.5. The wear rates of four coatings are 4.9 × 10–5, 4.2 × 10–5, 3.9 × 10–5 and 8.9 × 10–5 mm3·N−1·min−1, respectively. The coating of 15% WC has a minimum wear rate. When the WC content was 20%, its corrosion current density is the minimum (3.865 × 10–6 A·cm−2) and corrosion potential is the maximum (− 0.127 V), which has a good corrosion resistance. Therefore, when the WC content is maintained within 15–20%, the wear and corrosion resistance of the coating are synergistically enhanced. © The Indian Institute of Metals - IIM 2025.

The Cr-Zr-Cu copper alloy is widely used to manufacture mold for continuous casting. The proper coating can avoid the mold's failure under the condition of a high-temperature and friction environment. Three kinds of Inconel 718/WC-12Co coatings (micro-, nano-, and micro-nano-WC particles) were prepared on the surface of the copper alloy by laser. The phases, microstructure, and elemental distribution of L1-L3 coatings were observed and analyzed by x-ray diffractometer, scanning electron microscope, and energy dispersive spectrometer. The properties of L1-L3 coatings were tested by a Vickers hardness tester and friction and wear testing machine. The results show that the main phases are γ-Ni, M3W3C, MC, W0.15Ni0.85, and W2C in the L1-L3 coatings. In the L1 coating, there is an obvious phenomenon of WC agglomeration. In the L2 coating, there are many columnar, dendritic compounds, and "fish-bone" crystals with small size due to the addition of nanoparticles. In the L3 coating, the structure is scattered due to the uneven distribution of compounds. The average values of L1-L3 coatings' microhardness are 709.6, 851.9, and 600.1 HV0.5, respectively. The L2 coating has the maximum average microhardness. When the experimental temperature is 400 °C during the friction and wear test, the wear rates of L1-L3 coatings are 3.29, 1.89, and 2.83 × 10−4 mm3 N−1 mm−1, respectively. The L2 coating has the minimum wear rate due to the smaller grain size, denier microstructure, and "fish-bone" structure. © 2025 Author(s).

Longitudinal cracks are a common defect on the surface of continuous casting slabs, and cause increases in additional processing costs or long-time interruptions. The accurate identification of surface longitudinal cracks is helpful to ensure the casting process is adjusted in time, which significantly improves the quality of slabs. In this research, the typical temperature characteristics of thermocouples at the position of longitudinal cracks and their adjacent locations were extracted. The principal component analysis (PCA) method was used to reduce the dimensions of these characteristics to remove the redundant information. The particle swarm optimization (PSO) method was introduced to optimize the parameter. On this basis, a recognition model of surface longitudinal cracks was established, based on a particle swarm optimization-eXtreme gradient boosting (XGBOOST) model. Finally, this model was trained and tested using longitudinal crack and non-longitudinal crack samples and compared with the decision tree, the gradient boosting decision tree (GBDT) and XGBOOST models. The test results showed that PSO-XGBOOST had the best identification performance in all evaluation indexes. The accuracy, F1 score and alarm rate results were 95.8%, 92.3% and 100%, respectively, and the false alarm rate was as low as 5.5%. The research results provide a theoretical basis and a reliable model for surface longitudinal crack identification.

The parameters of laser cladding have a major impact on the quality of coating. The suitable parameters are helpful to improve the coating's morphology and properties. In this paper, a multi-objective optimization method is proposed to obtain the optimal parameters of laser cladding based on response surface methodology (RSM) and experiments. The laser power, scanning speed and preheating temperature are used as input factors, while coating's height, depth and hardness are used as target responses. According to ANOVA, the second-order model between the target response and input factors is established to analyze the influence of input factors on height, depth and hardness. Then a multi-objective optimization model is built up to obtain the optimal process parameters of laser cladding. Finally, a coating is successfully prepared with those parameters. The height, depth and hardness of coating are analyzed. The experimental results show that the laser power and preheating temperature have more influence on copper alloy coating. The optimal process parameters are laser power 1400 W, scanning speed 120 mm/min and preheating temperature 200 °C. The corresponding height, depth and average hardness of coating are 0.48 mm, 0.12 mm and 941.6 HV0.5, respectively. © 2023 Elsevier Ltd

The longitudinal crack is a common and serious defect on the surface of wide and heavy slab. The mould heat transfer and friction characteristics of 28 surface longitudinal cracks are collected and investigated in order to reveal the rule of the surface longitudinal cracks. The results show that the decrease amplitude of temperature in the presence of longitudinal crack is between -4.0 and -22.6 degrees C, and the increase amplitude of temperature is between 3.4 and 28.2 degrees C. The decrease of temperature velocity is between -0.4 and -1.5 degrees C.s(-1), while the increase of temperature velocity is between 0.32 degrees C.s(-1) and 1.64 degrees C.s(-1). When longitudinal cracks occur in mould, the heat flux of 21 cases has a decrease more than -0.02 MW center dot m(-2). There are 18 abnormal fluctuations of mould's transient friction during occurrence of the surface longitudinal crack, which is more than the stable casting. And there are 85.7% longitudinal cracks, which has an upward trend of friction tension or a downward trend of friction pressure.

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In order to improve the wear resistance and service life of die steel, Ni-based alloy coatings with different amount of WC–TiC ceramic particles were fabricated on the substrate of Cr12MoV die steel by laser. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to analyze the microstructures and phases of four coatings. The results show that four coatings have a good metallurgical bonding with the substrate and no crack and porosity on the surface. The reinforced phases were mainly γ~(Fe, Ni), Cr23C6, WC and Cr2Ti. The microstructure was mainly columnar dendrite, cellular dendrite and equiaxed crystal. When the mass fraction of WC particles was 40%, equiaxed crystal appeared in the coating. The WC and TiC particles were evenly distributed among γ~(Fe, Ni) and Cr23C6 phases. With the increase of WC mass fraction, the values of microhardness increased significantly, which were 680.5, 704.3, 752.6 and 806.4 HV0.5, respectively. The coating of 40% WC particles had the maximum microhardness (806.4 HV0.5). The wear volumes of four coatings were 0.47, 0.44, 0.26 and 0.40 mm3, respectively. With the increase of WC content, the wear resistance increased firstly and then decreased. When the mass fraction of WC particles was 30%, the coating had the minimum wear volume (0.26 mm3) and obtained the best wear resistance. It can be seen that the proper amount of WC and TiC ceramic particles enhanced the wear resistance of laser cladding coating. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

连铸坯裂纹的形成源于钢液凝固过程中的传热、流动和收缩等复杂行为,不仅与钢种的凝固特性及高温力学性能有着密切的联系,同时受铸坯的非均匀传热、收缩和摩擦等机械作用的影响。因此探索铸坯裂纹的形成机理及影响因素,对稳定和提升连铸坯质量具有重要意义。作为连铸工艺优化和开发的重要手段,以有限元法为代表的基于网格的模拟方法在调控复杂冶金过程、稳定和提升连铸坯质量等方面发挥了重要作用。然而,基于网格的模拟方法需要将问题域离散为单元或网格,在每个单元内分别对控制方程组进行求解,算法固有的网格依赖性,使其在处理曲线边界、相变移动界面和大变形等问题时,网格的重构与自适应十分复杂,且易产生网格畸变,给计算精度带来显著影响。与有限元等基于网格和拓扑结构的数值计算方法相比,无网格法仅通过节点离散计算域,计算域中任意点的场变量函数可通过其局部支持域内的场节点构造和描述,避免了复杂的剖分过程,在模拟和分析相变界面追踪、裂纹动态扩展方面体现出显著优势。鉴于此,本文基于无网格伽辽金方法,分别建立了连铸坯传热/凝固、变形/应力及裂纹萌生和扩展数值计算模型,运用C++程序设计语言开发出专用计算程序,依据现场实测结晶器热流,对圆坯的传热、变形和应力进行了计算和分析,考察了铸坯裂纹的萌生、扩展行为及规律特征,主要研究内容及结论包括:（1）基于无网格伽辽金法的圆坯传热/凝固模型开发和计算。采用移动最小二乘法近似构造温度场函数,依据变分原理推导了全局弱式的离散方程及时间离散格式,建立了基于无网格伽辽金法的圆坯二维横截面传热计算模型。探讨了模型空间和时间离散中重要参数对计算结果的影响,量化分析了圆坯非均匀传热过程的温度分布特征和坯壳生长规律。结果表明,采用完全隐式的欧拉向后时间差分格式情况下,均匀和随机节点布置都可以满足计算精度的要求;当时间步长小于1.0 s、平均节点间距5.63 mm和尺度参数αs为1.9时,模型具有较高的计算精度和效率;弯月面下70～120 mm为局部高热流区,非均匀程度最为显著,结晶器出口处铸坯表面的温度差值约150.0℃;受传热在水平方向的非均匀性和浇铸方向累积作用的双重影响,铸坯和结晶器间的传热总量决定了坯壳的厚度分布。（2）基于无网格伽辽金法的圆坯热弹塑性应力模型开发与计算。依据热弹塑性变形理论,采用增量形式处理铸坯在弹性和塑性变形阶段的本构方程,对弹塑性过渡区的校正方案进行了探讨。基于平面应力假设,采用移动最小二乘近似构造位移场函数,建立了基于无网格伽辽金法的铸坯应力计算模型。在本文实验和计算条件下,坯壳变形量和热流密度变化趋势基本一致,出口处坯壳表面变形量最大约0.78 mm,最小约0.21 mm,平均等效应力为14.8 MPa;坯壳径向应力分量表现为压应力,周向冷却强度低的区域,坯壳较薄,周向应力分量表现为拉应力,弯月面下50～150 mm为裂纹形成的敏感区域。（3）圆坯裂纹萌生和扩展数值模型的开发和计算研究。在圆坯无网格伽辽金传热、应力模型的基础上,建立了连铸圆坯裂纹萌生和扩展数值模型。模型通过定义局部裂纹检测子域和裂纹指数确定裂纹源的萌生位置,运用衍射法处理不连续的位移场近似,采用最大周向应力准则判断裂纹是否失稳扩展,而后根据应力强度因子提取裂纹扩展的方向,通过坐标变换完成裂纹几何形貌的更新。利用建立的模型对裂纹形成的动力学行为、场变量分布和影响因素等进行了计算和分析。结果表明,裂纹萌生于结晶器内高热流区内周向局部热流的峰值区域,扩展集中在弯月面下110～300mm,最终长度约为2～3 mm,裂纹平均扩展速率约为0.33～0.35 mm/s。当径向应力分量为拉应力时,铸坯沿径向被拉开,裂纹沿圆坯周向扩展;当周向应力分量为拉应力时,铸坯沿周向被拉开,裂纹沿圆坯径向扩展。

The copper alloy is widely used to prepare pipes in ocean engineering. The surface is washed and corroded by seawater for a long time, which gradually shortens the service life of the condenser tube. In order to improve the wear and corrosion resistance of copper alloy, a Ni60-WC coating was fabricated on a preheated copper alloy by laser cladding. Experiments on the Ni60-WC coatings were carried out by SEM, XRD, Vickers-microhardness meter, wear tester and electrochemical workstation. The microstructure, phases, hardness, wear and corrosion resistance were investigated. The results show that from the top to bottom, the microstructures were columnar dendrites, dendritic crystals and grains, respectively. The wear rate of the Ni60-WC coating was only 4.9 x 10(-5) mm(3)center dot N-1 center dot m(-1), which was only 1.14% of copper substrate. In addition, the corrosion current density was 2.34 x 10(-7) mA center dot mm(-2), which was much lower than that of copper alloy substrate (1.14 x 10(-6) mA center dot mm(-2)). The experimental results show that this Ni60-WC coating has a good metallurgical bonding and hardness, and it also has good wear and corrosion resistance, which is helpful to improve the service life of the condenser tube.

The coating on copper plate is difficult to be fabricated by laser. In order to obtain the optimal parameters of laser cladding coating, the temperature fields at different laser power and scanning speed were investigated and analyzed. The optimal parameters were selected with the depth and width of molten pool and compared with the experimental results. Then, the cooling rate, temperature gradient and solidification rate were calculated and analyzed with the coating's microstructure. The results show that the optimal process parameters are 1500 W and 2 mm/s. And at these parameters, the temperature field is consistent with the morphology of cladding coating. From bottom to top of the coating, the corresponding cooling rates are 1056.7, 936.5 and 762.6 degrees C/s, and the microstructure are elongated disordered dendrites, columnar dendrites and planar crystals, respectively.