本文選題：激光熔覆 + 灰鑄鐵　； 參考：《中國石油大學(xué)(華東)》2015年碩士論文

【摘要】：鑄鐵以其良好的性能廣泛應(yīng)用于重型裝備,鑄鐵表面激光熔覆加工可以有效提高鑄鐵裝備使用性能。由于工況惡劣,熔覆結(jié)合區(qū)易產(chǎn)生微裂紋不斷演化為宏觀裂紋,石墨相是鑄鐵的重要組成部分并未得到深入的研究,石墨相形態(tài)與聚集方式對熔覆結(jié)合強度與微裂紋萌生產(chǎn)生很大影響。本課題以分析鑄鐵激光熔覆過程中石墨相應(yīng)力特征,明確最優(yōu)激光工藝參數(shù)為目標(biāo),探尋石墨相應(yīng)力影響因素與裂紋萌生機制,確定最優(yōu)激光工藝參數(shù)。主要開展了以下內(nèi)容的研究工作:為探究與熔覆材料相容特性,選用鐵基熔覆合金粉末進行鑄鐵表面激光熔覆實驗,分析熔覆試樣結(jié)合區(qū)組織特性、石墨相形態(tài)特征及石墨相尖端微裂現(xiàn)象。通過采用剪切實驗裝置對熔覆試樣進行測試,計算單位面積基體與熔覆層平均結(jié)合強度,明確石墨相周圍區(qū)域組織及微裂紋對熔覆質(zhì)量的影響機制。根據(jù)熔覆實驗實際工況,對激光熱源進行改進,采用生死單元技術(shù)實現(xiàn)粉末動態(tài)添加,建立激光熔覆熱力耦合模型,分析激光熔覆熱響應(yīng)規(guī)律。采用正交試驗對鑄鐵激光熔覆過程仿真模擬,提取激光熔覆結(jié)合區(qū)最大殘余應(yīng)力影響因素,指導(dǎo)激光熔覆工藝方案制定,為石墨相微觀模型的建立提供數(shù)據(jù)支持。為明確石墨相尖端微裂紋萌生機理,根據(jù)鑄鐵激光熔覆實驗與熱力耦合模型,建立石墨-環(huán)境相微觀模型,研究石墨長度、尖端角度等形態(tài)參數(shù)和對接、平行、垂直等聚集方式對石墨相尖端應(yīng)力影響規(guī)律,定量分析石墨相應(yīng)力變化特征。以激光熔覆熱力耦合模型和石墨-環(huán)境相微觀模型為基礎(chǔ),結(jié)合正交試驗設(shè)計方法,分析激光熔覆裂紋萌生影響因素,考慮鑄鐵激光熔覆過程石墨相作用,分別從結(jié)合區(qū)殘余應(yīng)力角度與石墨相尖端應(yīng)力角度確定最優(yōu)激光工藝參數(shù),降低應(yīng)力,進一步減少裂紋萌生,提高熔覆質(zhì)量。
[Abstract]:Cast iron is widely used in heavy equipment due to its good properties. Laser cladding on cast iron surface can effectively improve the performance of cast iron equipment. Because of the bad working conditions, microcracks in the cladding bonding zone tend to evolve into macroscopic cracks, and the graphite phase is an important part of cast iron has not been deeply studied. The morphology and aggregation mode of graphite have great influence on the cladding bonding strength and micro-crack initiation. The aim of this paper is to analyze the corresponding force characteristics of graphite in laser cladding process of cast iron, to determine the optimum laser process parameters, to explore the influencing factors of graphite corresponding force and the mechanism of crack initiation, and to determine the optimal laser technological parameters. The main research work is as follows: in order to study the compatibility with cladding materials, iron-base cladding alloy powder is selected for laser cladding experiment on cast iron surface, and the microstructure of the bonding zone of cladding sample is analyzed. The morphologic characteristics of graphite phase and the phenomenon of microcrack at the tip of graphite phase. The average bonding strength between the matrix and the cladding layer was calculated by means of the shear test device, and the influence mechanism of the microstructure around the graphite phase and the micro-crack on the cladding quality was determined by calculating the average bonding strength between the matrix and the cladding layer per unit area. According to the actual condition of cladding experiment, the laser heat source is improved, the powder dynamic addition is realized by the birth and death element technique, the coupled thermal model of laser cladding is established, and the thermal response law of laser cladding is analyzed. The process of laser cladding of cast iron was simulated by orthogonal test. The factors affecting the maximum residual stress in laser cladding bonding zone were extracted to guide the formulation of laser cladding process and to provide data support for the establishment of micro model of graphite phase. In order to clarify the mechanism of micro-crack initiation at the tip of graphite phase, a graphite-environmental micromodel was established according to the coupled model of laser cladding and thermodynamics of cast iron. The morphological parameters such as graphite length and tip angle were studied and parallel to each other. The effect of vertical equiaggregation mode on the stress at the tip of graphite phase is studied and the variation characteristics of graphite corresponding forces are quantitatively analyzed. Based on the thermal coupling model of laser cladding and the graphite-environment microcosmic model, combined with the orthogonal test design method, the factors affecting laser cladding crack initiation were analyzed, and the graphite phase action in laser cladding process of cast iron was considered. The optimum laser processing parameters are determined from the angle of residual stress in bonding zone and the angle of stress at the tip of graphite phase, which can reduce the stress, further reduce the crack initiation and improve the quality of cladding.
【學(xué)位授予單位】：中國石油大學(xué)(華東)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG174.4

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