高温合金是现代航空发动机、航天器和火箭发动机以及工业燃气机轮的关键热端部件材料，也是核反应堆、化工设备等方面不可或缺的重要高温结构材料，镍基高温合金以更高的高温强度和组织稳定性在整个领域占有重要的地位。但高温合金零件存在成形形状复杂，传统材料加工方法难以实现的问题。激光熔覆技术提供了一种有效的手段制备几何结构复杂的零部件，且可以通过在廉价、易加工的工件表面制备高性能的涂层来降低生产成本，近年来得到了广泛的应用。由于激光熔覆是一个多物理、多尺度现象同时发生的过程，受多种因素共同影响，如何获得尺寸精度高、力学性能好的熔覆涂层仍是当前研究领域的一个热点。然而，各因素之间既独立又非线性相关，同时考虑所有因素非常困难。其中，工艺参数作为最直接的影响因素，分析其对熔覆质量的影响具有重要的现实意义和工程价值。

    本文选择光斑形状、激光功率、扫描速度和基体温度为对象，研究了它们对熔覆过程中温度-应力-应变场演变的影响。以激光功率、扫描速度和送粉速率为参数进行了激光熔覆Ni45合金粉末的实验，研究了熔覆层形貌、凝固组织和显微硬度的变化。基于实验结果，采用PCA-TOPSIS的方法对工艺参数进行了优化，分析了三个工艺参数对熔覆层形貌的影响程度。主要的研究内容和结论如下：

1.建立了同步送粉激光熔覆三维模型，对熔覆过程中进行模拟，研究了光斑形状、激光功率、扫描速度和基体预热温度对温度-应力场-应变场演化的影响。通过对定义路径上的温度、温度梯度、冷却速度、应力及应变的分布的分析，得到各工艺参数对熔覆过程的影响规律，对预测涂层组织和性能提供了理论依据。

2.基于数值模拟的规律，设计了在316L不锈钢基体上激光熔覆Ni45合金粉末的实验。通过对熔覆层形貌、微观组织和显微硬度进行分析，研究了激光功率、扫描速度和送粉速率对熔覆质量的影响。稀释率作为侧面反映熔覆层性能的重要因素，与激光功率和扫描速度呈正相关，与送粉速率呈负相关，对稀释率进行控制是得到高性能熔覆层的关键。

3.采用基于主成分分析（PCA）的逼近理想解排序法（TOPSIS）在考虑因素之间相关性的基础上对实验进行了综合排序，得到了优化的工艺参数组合：激光功率700W、扫描速度3mm/s、送粉速率8.1g/min。通过分析得到，三个工艺参数对熔覆尺寸的影响程度由大到小依次为：送粉速率、扫描速度、激光功率。

Superalloy is an important material for hot components in modern aerospace engines, spacecraft and rocket engines, and industrial gas turbine wheels, and it is also indispensable for nuclear reactors and chemical equipment. Nickel-based superalloy plays an important role in the whole field with higher high-temperature strength and structural stability. However, the shape of superalloy parts is complex, and the traditional material processing methods are difficult to achieve. Laser cladding technology provides an effective means to prepare geometrically complex parts. At the same time, it can reduce production costs by preparing high-performance coatings on inexpensive, easy-to-machine workpiece surfaces, and has been widely used in recent years. Because laser cladding is a multi-physics, multi-scale phenomenon process, the processing quality is depend on many factors. How to obtain cladding coating with high precision and mechanical properties is still a hot topic in the current research field. Due to the independence and relevance of factors, it is hard to consider them at the same time. As the most direct influencing factor, it is of great practical significance and engineering value to analyze the influence of process parameters on the quality of cladding.

In this paper, the laser spot shape, laser power, scanning speed and substrate temperature are selected as the object, and under different heat input conditions, the effect of temperature-stress-strain field evolution during cladding were studied. The effects of laser power, scanning speed and powder feeding rate on the morphology, solidification structure and microhardness of laser cladding Ni45 alloy powder cladding layer were studied by experiments. Based on the experimental results, the process parameters were optimized by PCA-TOPSIS method, and the influence of three process parameters on the size of the molten pool was analyzed. The main research contents and conclusions are as follows:

A three-dimensional model of synchronous powder feeding laser cladding was established to simulate the cladding process. The effects of spot shape, laser power, scanning speed and preheating temperature were studied. Through the analysis of the distribution of temperature, temperature gradient, cooling rate, stress and strain on the defined path, the influence of process parameters on the cladding process is obtained, which provides a theoretical basis for predicting the structure and properties of the coating.

Based on the law of numerical simulation, the experiment of laser cladding Ni45 alloy powder on 316L stainless steel substrate was designed. The effects of laser power, scanning speed and powder feeding rate on the quality of the cladding were studied by analyzing the morphology, microstructure and microhardness of the cladding layer. As an important factor that reflects the performance of the cladding layer. It is positively correlated with laser power and scanning speed, and negatively correlated with powder feeding rate. Controlling the dilution rate is the key to obtaining a high performance cladding layer.

The results of the experiment were comprehensively sorted by Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) that based on Principal Component Analysis (PCA). Considering the correlation between the factors, the optimized combination of process parameters was obtained: laser power 700W, scanning speed 3mm/s, and powder feeding rate 8.1g/min. In addition, the influence degree of three process parameters on the size of the cladding was analyzed, and the powder feeding rate, scanning speed and laser power were sequentially changed from large to small.