本文選題：激光表面強化　切入點：微觀組織　出處：《華中科技大學(xué)》2012年碩士論文　論文類型：學(xué)位論文

【摘要】：液壓油缸由于其工作環(huán)境的多為高溫、潮濕，因此其表面經(jīng)常會出現(xiàn)腐蝕，磨損等失效形式，而在修復(fù)過程中，如果采用整體更換則會使成本過高，因此人們多采用表面強化技術(shù)對其進行局部的修復(fù)以達到繼續(xù)使用的目的。而激光表面強化以其具有的諸多優(yōu)勢，在修復(fù)表面方面具有極大的前景。 本次課題采用光纖和CO2兩種激光器，以45鋼作為基材，進行激光表面強化實驗。研究激光表面強化合適的工藝參數(shù)和影響因素。對激光合金化試樣進行了XRD、SEM、硬度，耐蝕性和耐磨損性能檢測，并對激光處理的強化機制進行了探討 在顯微組織方面，經(jīng)SEM分析表明，激光淬火后表層組織區(qū)域可以分為熔化區(qū)和熱影響區(qū)兩部分，且均由馬氏體組織組成，但是熔化區(qū)的組織較粗大；激光合金化后表層組織區(qū)域由合金化區(qū)，過渡區(qū)和熱影響區(qū)三部分組成，合金化層由于溫度梯度和凝固速度之比的不同，由平面晶、胞狀晶、樹枝晶以及等軸晶組成。過渡區(qū)則是由細小針狀馬氏體組成，熱影響區(qū)主要由殘余奧氏體、馬氏體、珠光體和鐵素體組成。實驗所選用的激光種類和激光合金化中激光的參數(shù)都會對表層的結(jié)構(gòu)和其顯微組織造成影響。激光功率的加大和掃描速度的提高都能達到細化晶粒的效果。而激光熔覆之后截面可分為熔覆層，合金化層和熱影響區(qū)三個部分，，從熔覆層到熱影響區(qū)，組織逐漸由等軸晶，到樹枝晶，到胞狀晶，平面晶，最后到熱影響區(qū)的馬氏體組織，并且在添加WC的情況下，WC會呈雪花狀或片狀分布在熔覆層內(nèi)。 對表層的截面進行了硬度檢測，結(jié)果表明合金化層和熔覆層的顯微硬度相比基體都有了明顯的提高，分別可以達到500HV和900HV。在不影響激光處理的效果范圍內(nèi)增大激光功率或者提高激光掃描速度可以獲得較高的表層硬度。晶粒細化，合金元素的彌散強化和析出相的固溶強化。 對激光處理后的材料表層進行了耐磨性能和耐蝕性能的測試，發(fā)現(xiàn)經(jīng)過激光合金化和激光熔覆之后的涂層在耐磨和耐蝕性能上均有較大的提升，耐磨性能相比基體提升了5倍以上，激光工藝參數(shù)對材料的耐蝕性和耐磨性均有較大影響 在基體表面熔覆Fe基合金粉末和WC粉末混合的涂層之后發(fā)現(xiàn)耐蝕性有了稍微的下降，推測可能是由于WC粉末加入的比例對其耐蝕性有一定的影響。
[Abstract]:Because the working environment of the hydraulic cylinder is mostly high temperature and humidity, the surface of the cylinder is often damaged by corrosion and wear. In the repair process, if the whole replacement is adopted, the cost will be too high. Therefore, surface strengthening technology is often used to repair the surface in order to achieve the purpose of continued use, while laser surface strengthening has great prospects in repairing the surface because of its many advantages. In this paper, the laser surface hardening experiments were carried out with 45 steel as the substrate by using two kinds of laser fiber and CO2 lasers. The suitable technological parameters and influencing factors of laser surface strengthening were studied. The hardness of laser alloyed samples was studied. The corrosion resistance and wear resistance are tested, and the strengthening mechanism of laser treatment is discussed. In the aspect of microstructure, SEM analysis shows that the surface microstructure area after laser quenching can be divided into melting zone and heat affected zone, and both of them are composed of martensite structure, but the microstructure of melting zone is relatively large. After laser alloying, the surface layer is composed of alloying zone, transition zone and heat affected zone. The alloying layer is made up of plane crystal and cellular crystal due to the difference of temperature gradient and solidification rate. The transition zone is composed of fine acicular martensite, and the heat affected zone is mainly composed of residual austenite, martensite, The composition of pearlite and ferrite. The type of laser selected in the experiment and the laser parameters in laser alloying will affect the structure and microstructure of the surface layer. The increase of laser power and the increase of scanning speed can be achieved. The effect of grain refinement. After laser cladding, the cross section can be divided into cladding layer, The microstructure of alloying layer and heat affected zone from cladding to heat affected zone is gradually from equiaxed crystal to dendrite to cellular crystal, plane crystal, and finally to martensite structure of heat affected zone. When WC is added, the WC will be snowflake or flake in the cladding layer. The hardness of the surface section is tested. The results show that the microhardness of the alloying layer and the cladding layer are obviously improved compared with the matrix. The surface hardness, grain refinement, diffusion strengthening of alloy elements and solution strengthening of precipitated phase can be obtained by increasing laser power or laser scanning speed in the range of no effect of laser treatment, 500 HV and 900HV, respectively. The wear resistance and corrosion resistance of the laser treated coating are tested. It is found that the coating after laser alloying and laser cladding has a great improvement in wear resistance and corrosion resistance. The wear resistance of the material is more than 5 times higher than that of the matrix. The laser process parameters have great influence on the corrosion resistance and wear resistance of the material. It was found that the corrosion resistance decreased slightly after the coating of Fe-base alloy powder and WC powder mixed on the substrate surface, which may be due to the influence of the proportion of WC powder on the corrosion resistance.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2012
【分類號】：TH137.51;TG174.4


本文編號：1571792