【作者】 赵志平；

【导师】 李有堂；

【作者基本信息】 兰州理工大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 热喷涂技术做为一种表面强化技术,是表面工程技术的重要组成部分,一直是我国重点推广的新技术项目,随着科技发展,热喷涂技术目前在国内外已取得了比较广泛的推广应用。为了保证热喷涂构件的使用性能,以往人们主要关注的是热喷涂件的耐磨损性、耐腐蚀性、耐高温隔热性、电学、光学等性能,对热喷涂件整体疲劳性能及影响因素方面研究较少。本文通过对热喷涂成形过程及影响热喷涂件疲劳性能关键因素方面的系统研究,取得了如下成果：1.分析了热喷涂涂层微观成形机理,研究了热喷涂的燃烧火焰特性、喷涂粒子的速度特征及喷粉熔滴飞行过程中的氧化行为,确定了喷涂试样合理的工艺方案及参数。2.通过试验研究了不同重熔条件下火焰热喷涂件的弯扭疲劳性能,并对试样的宏观断口、微观断口、涂层组织成分、极限应力、疲劳扩展面积等方面进行了分析研究。结果表明：重熔时间长短是影响火焰热喷涂件疲劳性能的关键因素之当重熔时间合理时,火焰热喷涂件的弯扭疲劳寿命最长。当重熔时间不足时,涂层中Ni粉及Si粉颗粒大多没有熔融,Si粒与空气中的O发生化学反应生成Si02颗粒。同时,涂层表面强度、涂层内聚力、涂层与基体结合力均不强,导致疲劳寿命较短。当重熔时间过长时,涂层中的Si再次与O发生化学反应生成Si02颗粒,成主要疲劳裂纹源,且保温时间越长,颗粒越大,致使疲劳寿命降低。3.基体试样与重熔合理试样在弯扭疲劳试验中的疲劳裂纹扩展区面积S的对数(1gS)与疲劳寿命Nf的对数(1gN1)戎线性正比关系,相关系数分别为0.992和0.994。由此可以推断：对于火焰热喷涂重熔合理试样及基材试样可尝试根据扩展区面积来推算疲劳寿命。4.经不同重熔时间处理后涂层表面主要组成相为Cr7C3.Ni.Cr3Ni5Si2.CrB. Ni3B.随着重熔时间的变化,涂层表面硬质相的含量会出现变化。当重熔时间过长后涂层表面硬质相的含量明显降低。5.涂层厚度是影响火焰热喷涂件疲劳寿命的又一关键因素。对所设计试样而言,其合理的涂层厚度为0.25mm。当涂层厚度大于0.25mm时,热喷涂件的拉压疲劳寿命随厚度的增加而呈现总体下降的趋势,热喷涂件的拉压疲劳寿命与涂层中非金属颗粒及孔隙的数量及平均大小密切相关。涂层厚度合理时,涂层表面及界面相对于中间涂层部分承受较大的轴向拉压载荷,热喷涂件的拉压疲劳寿命在合理的重熔条件下,高于基体40Cr试样的疲劳寿命。这一试验结果说明研究火焰热喷涂件的疲劳寿命具有实际的应用价值。6.重熔时间也是决定火焰热喷涂件涂层磨损性能及涂层表面硬度的关键因素。经重熔2min、5min、10min及12min后涂层表面显微硬度分别为：340HV、385HV、455HV及400HV。涂层磨损体积分别为：3.734×107μm3、3.50974×107μm3、3.029×107μm3及3.266×107μm3。以上试验结果表明：当重熔时间合理时,涂层表面显微硬度及涂层耐磨损能力最强。同时分析表明：涂层的磨损机理主要为磨粒磨损和疲劳磨损。7.应用一种能将高周疲劳和低周疲劳统一表征的能量形式表征参量对不同重熔处理下热喷涂件的低周疲劳寿命进行了预测。预测结果与试验结果符合较好。说明：应用能量法则来进行疲劳寿命的预测能够揭示疲劳损伤的本质,具有较高的准确性,并且物理意义明确,对疲劳寿命评估具有重要的实际意义。更多还原

【Abstract】 The thermal spraying technology which as a surface strengthening technology is one of surface engineering technology, and its development and promotion have been given priority in china. With the development of science and technology the thermal spraying technology has been made extensive popularization and application at home and abroad. In order to guarantee the usability of thermal spraying component, people mainly focused on wear resistance, corrosion resistance, high temperature resistant and heat insulation performance, electrical and optical properties, etc. The fatigue performance and affecting factors on fatigue of thermal spraying component were rarely concerned. In this paper, the forming process of thermal spray and the affecting factors of fatigue performance were studied, and some important results were obtained as follow:1. The micro-mechanism of thermal spraying coating forming was analyzed, burning flame characteristics of thermal spraying, speed characteristics of spraying particles, oxidation behavior of spray molten droplets in the process of the flight were researched, the reasonable process scheme and spraying parameters of thermal spraying component were determined.2. The combined bending and torsion fatigue life of the sample which were remelted under different remelting time conditions were investigated by test. The macrofracture and the microfracture of samples, coating composition, limit stress, fatigue extension area were analyzed. The results show that the reasonable remelting time is the key factor to decide the performance of combined bending and torsion fatigue of thermal spraying components. The components have the longest fatigue life when remelting time is reasonable. The shorter remelting time the lower fatigue lifetime resulting from loose coating, lower strength of coating surface and the interface of coating and substrate and SiO2particles produced by unfused Si particles reacted with Oxygen. The longer remelting time the lower fatigue lifetime owing to reproduced particles of SiO2that as the source of crack, and the longer soaking time, the shorter fatige lifetime of components.3. The logarithmic value (lgS) of fatigue crack propagation region area(S) is proportional to logarithmic value(1g N1) of fatigue life of base samples and spraying samples with reasonable remelting time, and the correlation coefficient is0.992and0.994, respectively. Thus it can be inferred that the size of the propagation region area can be used to estimate the fatigue life of samples with reasonable remelting time.4. The main composition of coating with different remelting time are Cr7C3、Ni、 Cr3Ni5Si2、CrB、 Ni3B. The content of different composition of coating surface was changed with different remelting time. The content of hard phase of coating surface was decreased obviously after longer remelting time.5. The coating thickness is another key factor to decide the fatigue life of flame thermal spraying components. The reasonable coating thickness is0.25mm for the designed samples. The stretching and compression fatigue lifetime of flame thermal spraying components was decreased with the increase of the thickness of coating when the thickness of coating is more than0.25mm. The fatigue lifetime of components is closely related to the number and the average size of nonmetallic particles and pores. The interface and the surface of coating endure more loads of stretching and compression than the middle coating when the coating thickness and the remelting time are reasonable, so the stretching and compression fatigue lifetime of thermal spraying samples is longer than matrix samples. The test results show that the research on fatigue lifetime of flame thermal spraying component has practical application value.6. The remelting time is a key factor to decide the wear resistance and surface hardness of coating of thermal spraying components. The surface hardness of coating with remelting time of2min,5min,10min and12min is340HV,385HV,455HV,400HV, respectively, and the corresponding wear volume of coating is3.734X107μm3、3.50974×107μm3、3.029×107μm3、3.266×107μm3, respectively. The test results show that the surface micro-hardness and the wear resistance ability of coating are strongest when the remelting time is reasonable. The wear mechanism of coating is mainly abrasive wear and fatigue wear.7. An energy model for a characterization parameters of energy form that can characterize the fatigue life of low and high cycle fatigue simultaneously was used to forecast the LCF life of thermal spraying components with different remelting time, the predicted results were consistent with the experimental results. The result show that using the law of energy to forecast the fatigue life of coating components can reveal the nature of the fatigue damage, the results has higher accuracy and clear physical meaning, so it has important practical significance to evaluate the life time of cycle fatigue.更多还原