Study on Laser Cladding NiAl/Al2O3 Coating on Magnesium Alloy

利用等离子喷涂技术,在AZ91D镁合金表面制备NiAl/Al2O3涂层,并通过激光对涂层进行重熔处理。利用X射线衍射(XRD)和扫描电镜(SEM)测试手段分别研究了涂层在激光重熔前后的相组成和形貌,涂层的结合强度和孔隙率分别采用拉伸法和光学显微镜(OM)测量,利用显微硬度计测量重熔前后涂层的显微硬度。结果表明:经激光重熔处理后,NiAl过渡层与基体及Al2O3涂层界面处出现了具有冶金结合的特征,涂层的结合强度由原来的11.34提高到33.2MPa;涂层的孔隙率则由原来的10.23%下降到4.10%,涂层变得更致密;涂层中的亚稳相γ-Al2O3全部转变为稳定相α-Al2O3;涂层的显微硬度HV0.05由3290MPa提高到5200MPa,有利于其耐磨性的提高。     

镁合金AZ91HP表面激光重熔Al2O3涂层的组织及性能

采用等离子喷涂和激光重熔复合工艺在AZ91HP镁合金表面制备了Al2O3陶瓷涂层.结果表明,由于受激光作用区温度场分布、陶瓷材料热物性参数和涂层厚度等因素的综合影响,激光重熔Al2O3涂层呈现出明显的分层结构特征.依据组织结构不同,可将其分为:由α-Al2O3柱状晶构成的表面熔凝区、具有团絮状形貌特征的烧结区以及保持原喷涂态结构特征的残留等离子喷涂层.由于激光重熔陶瓷涂层表面单相α-Al2O3柱状晶的形成,使其硬度及耐磨、耐蚀性均明显优于等离子喷涂Al2O3涂层和原始镁合金.     

激光重熔与冷喷涂复合工艺制备的镍铝青铜基涂层耐腐蚀性能研究

为解决镍铝青铜质螺旋桨修复再制造难题,使用激光重熔加冷喷涂复合工艺在镍铝青铜9442合金上制备了Cu402F涂层。使用OM、SEM观察了涂层截面与表面的微观形貌;采用盐雾腐蚀箱、电化学工作站重点研究了涂层的耐盐雾腐蚀性能和电化学行为。试验结果表明:冷喷涂态涂层厚度约为300μm,涂层致密度良好,表面较为粗糙,经过激光重熔后涂层表面变得较为平整,涂层内部分为重熔区、多孔过渡区以及冷喷涂遗传区;经1 000h中性盐雾腐蚀试验后,冷喷涂态涂层腐蚀产物呈现菜花状,表面存在着大量裂纹,激光重熔态腐蚀产物呈圆形颗粒状,表面出现点蚀坑,激光重熔后涂层失重量减少了43.86%,耐盐雾腐蚀性能增强;涂层在浸泡不同时间后动电位极化曲线可知,冷喷涂态涂层在浸泡5天后涂层上就逐渐形成钝化膜,并且随着浸泡时间的增加,涂层上的钝化膜更加稳定,激光重熔态涂层浸泡36天后表面可以形成十分稳定并且具有一定厚度的钝化膜,耐海水腐蚀性能大幅提高。     

镁合金等离子喷涂Al/Al_2O_3涂层的耐腐蚀性能

采用等离子喷涂技术在AZ31镁合金表面制备Al/Al_2O_3复合涂层,测试了镁合金及表面喷涂有Al/Al_2O_3复合涂层的镁合金试样的极化曲线,研究了没有涂层、经封孔处理和未经封孔处理的喷涂有复合涂层的镁合金三种试样在浸泡腐蚀和5%NaCl盐雾腐蚀情况下的耐腐蚀性能及其腐蚀行为.结果表明,经封孔处理的Al/Al_2O_3复合涂层镁合金试样在上述腐蚀条件下的耐腐蚀性均优于镁合金和涂层未封孔处理的试样,在浸泡试验中未封孔处理的涂层试样比镁合金腐蚀更加严重,在盐雾试验中却优于镁合金.     

汽车发动机用AZ91合金表面喷涂与性能研究

采用等离子喷涂和激光重熔法在汽车发动机用AZ91合金表面制备了不同涂层,对比研究了涂层表面和横截面形貌、物相组成、显微硬度和电化学性能。结果表明,等离子喷涂层物相为:γ-Ni、FeNi_3、Ni_3B、WC、W_2C和Cr_7B_3,激光重熔层物相为γ-Ni、CrB、Ni_4B_3、WC、Cr_(23_B6和Cr_2B_3;显微硬度由高到低依次为:激光重熔层等离子喷涂层Ni/Al过渡层AZ91合金基材;等离子喷涂层和激光重熔层的耐腐蚀性能均高于AZ91合金基材,且激光重熔层的耐腐蚀性高于等离子喷涂层。     

钛合金表面激光重熔等离子喷涂陶瓷涂层研究

采用等离子喷涂和激光重熔复合工艺在钛合金(TC4)表面制备了Al2O3+13%TiO2质量分数陶瓷涂层,研究了激光重熔对陶瓷涂层的微观结构、显微硬度及结合强度的影响.结果表明经激光重熔以后,基本消除了由于等离子喷涂形成的层状堆积结构,涂层表面形成了均匀细密的棒状组织,大幅减少了孔隙率.经过实验检测.激光重熔后的涂层结合力比喷涂涂层的提高近2倍.     

激光重熔对TiAl合金表面等离子喷涂热障涂层耐热腐蚀性能的影响

分别采用等离子喷涂和等离子喷涂一激光重熔复合工艺在TiAl合金表面制备了热障涂层,研究了两种涂层在850℃：下75％Na2SO4＋25％NaCl（质量分数）熔融盐中的热腐蚀行为,进而分析激光重熔工艺对等离子喷涂热障涂层耐热腐蚀性能的影响。结果表明：激光重熔热障涂层可以有效地阻止熔融盐腐蚀介质进入涂层发生腐蚀,具有更优的抗热腐蚀性能和使用寿命。     

TC4钛合金表面等离子喷涂Al2O3-13wt%TiO2涂层及激光重熔研究

采用等离子喷涂技术在TC4钛合金表面制备了常规Metco130陶瓷涂层及纳米结构Al2O3-13wt%TiO2涂层,并利用CO2激光器对涂层进行了激光重熔,采用X射线衍射分析(XRD)、扫描电镜分析(SEM)、微区成分分析(EDAX)及维氏硬度试验研究了激光重熔前后涂层的组织性能变化.结果表明,等离子喷涂涂层与基体形成了较好的机械结合,但涂层中存在孔隙,激光重熔后,重熔层与基体形成了良好的冶金结合,其组织结构更为均匀而致密.采用谢乐公式估算了重熔后涂层中各相的平均粒径,结果表明,等离子喷涂纳米结构的涂层在激光重熔后仍然处于纳米结构.另外,选择合理的激光工艺参数,涂层的硬度得到了较大提高.     

镁合金表面等离子喷涂+激光重熔Al-Si基纳米Si_3N_4复合涂层

为了改善镁合金表面的性能,将等离子喷涂和激光重熔技术相结合,利用5 kW横流连续CO2激光器,在AZ31B镁合金表面进行了激光重熔Al-Si+1%nano-Si3N4等离子喷涂复合涂层的试验研究。通过扫描电子显微镜、能谱分析仪、X射线衍射仪分析了重熔层的组织、成分分布和重熔前后的物相及结合界面,用显微硬度仪和电化学工作站测试并对比复合涂层重熔前后的硬度和腐蚀性能。结果表明,等离子喷涂层经激光重熔后与镁基体达到了良好的冶金结合,在激光作用下,重熔层析出的金属间化合物AlN、Mg2Si及弥散的铝硅固溶体强化相有效提高了其显微硬度,最高值达到514 HV0.05,是基体的10倍。在析出强化相作用下,重熔层的耐蚀性得到明显提高,自腐蚀电流较喷涂层和镁基体降低一个数量级。     

激光重熔纳米Al2O3-13%TiO2陶瓷涂层组织及性能

为了进一步提高等离子喷涂纳米Al2O3-13%TiO2(质量分数, 下同)复合陶瓷涂层的性能,在γ-TiAl基体材料表面采用激光重熔工艺对涂层进行处理,研究了激光重熔对涂层微观组织和性能的影响.用扫描电镜(SEM)和显微硬度计分析了涂层形貌、微观结构和显微硬度,同时对涂层的磨损特性进行了考察.结果表明,等离子喷涂纳米陶瓷涂层由纳米颗粒完全熔化区和部分熔化区两部分组成,仍然具有等离子喷涂态的典型层状结构.经过激光重熔后,形成了致密细小的等轴晶重熔区、烧结区和残余等离子喷涂区,由于激光快速加热和快速冷却加工特点,在重熔区仍保留了部分来源于原等离子喷涂部分熔化区的残留纳米粒子.与常规等离子喷涂陶瓷涂层相比,纳米结构涂层可在一定程度上提高其硬度和耐磨性,经过激光重熔后其硬度和耐磨性进一步提高.     

激光表面重熔对热喷涂铝涂层微观结构及其阻氢性能的影响

采用Ｘ射线衍射仪、扫描电镜及热充氢等方法,研究了激光重熔对不锈钢表面热喷涂铝涂层的微观结构及其阻氢性能的影响。结果表明,激光重熔后涂层组织均匀、致密,主要由ＡｌＦ３（Ｎｉ,Ｃｒ）固溶体、ＣｒＦｅＮｉ奥氏体等相组成,而且涂层与基体形成了良好的冶金结合。此外,激光表面重熔后涂层的阻氢性能亦得到改善。     

激光重熔等离子喷涂Al2O3–13 %TiO2涂层的组织结构

采用等离子喷涂方法制备Al2O3–13%TiO2涂层,对涂层进行激光重熔处理。利用电子扫描显微镜(SEM)观察涂层断口组织,金相截面组织和金相表面组织形貌,分析激光重熔处理后涂层的凝固过程。结果表明:激光重熔处理,使涂层由块状结构转变为平行排列,垂直于基体方向生长的柱状晶和柱状枝晶结构。由于金属基体温度低、散热快,使得陶瓷涂层上下温差大,诱发了陶瓷晶粒的定向生长,这是使陶瓷晶粒垂直于基体生长的主要原因。     

Improving corrosion properties of high-velocity oxy-fuel sprayed inconel 625 by using a high-power continuous wave neodymium-doped yttrium aluminum garnet laser

Thermal spray processes are widely used to protect materials and components against wear, corrosion and oxidation. Despite the use of the latest developments of thermal spraying, such as high-velocity oxy-fuel (HVOF) and plasma spraying, these coatings may in certain service conditions show inadequate performance,e.g., due to insufficient bond strength and/or mechanical properties and corrosion resistance inferior to those of corresponding bulk materials. The main cause for a low bond strength in thermalsprayed coatings is the low process temperature, which results only in mechanical bonding. Mechanical and corrosion properties typically inferior to wrought materials are caused by the chemical and structural inhomogeneity of the thermal-sprayed coating material. To overcome the drawbacks of sprayed structures and to markedly improve the coating properties, laser remelting of sprayed coatings was studied in the present work. The coating material was nickel-based superalloy Inconel 625, which contains chromium and molybdenum as the main alloying agents. The coating was prepared by HVOF spraying onto mild steel substrates. High-power continuous wave Nd:YAG laser equipped with large beam optics was used to remelt the HVOF sprayed coating using different levels of power and scanning speed. The coatings as-sprayed and after laser remelting were characterized by optical microscopy and scanning electron microscopy (SEM). Laser remelting resulted in homogenization of the sprayed structure. This strongly improved the performance of the laser-remelted coatings in adhesion, wet corrosion, and high-temperature oxidation testing. The properties of the laser-remelted coatings were compared directly with the properties of as-sprayed HVOF coatings and with plasma-transferred arc (PTA) overlay coatings and wrought Inconel 625 alloy.     

基于划痕实验激光重熔Ni基WC金属陶瓷涂层强度分析

目的进一步提高以45#钢为基体的等离子喷涂Ni基WC金属陶瓷涂层综合性能。方法采用不同激光重熔工艺参数对涂层进行处理,通过划痕实验测定涂层的内聚强度和与基体的结合强度,前者由划痕实验中的锥形投影面积确定,内聚强度与锥形投影面积成反比,后者根据划痕仪反馈数据临界载荷L_c确定。结果 300 W激光重熔后,涂层锥形投影面积A为101,小于重熔前的276,即涂层内聚强度提高。激光重熔后的临界载荷L_c为68 N,大于重熔前的45 N,涂层与基体的结合强度增大。300、800、1200 W激光功率下,涂层锥形投影面积分别为101.6、56.7、198.0,临界强度分别为68、77、41 N。激光功率达到1500 W时,涂层脱落。即本试验数据中,激光功率为800 W时,涂层的内聚强度和结合强度最佳。结论激光重熔等离子喷涂Ni-WC金属陶瓷涂层后,涂层内聚强度和结合强度都有显著提高。不同的激光参数对涂层的性能有很大差别,适当的参数范围可达到理想效果,若激光功率参数取值过大,涂层产生的残余应力大于内聚力时会导致涂层脱落,反而降低涂层性能。     

Corrosion behavior of HVOF-sprayed and Nd-YAG laser-remelted high-chromium,nickel-chromium coatings

Thermal spray processes are widely used to deposit high-chromium, nickel-chromium coatings to improve high temperature oxidation and corrosion behavior. However, despite the efforts made to improve the present spraying techniques, such as high-velocity oxyfuel (HVOF) and plasma spraying, these coatings may still exhibit certain defects, such as unmelted particles, oxide layers at splat boundaries, porosity, and cracks, which are detrimental to corrosion performance in severe operating conditions. Because of the process temperature, only mechanical bonding is obtained between the coating and substrate. Laser remelting of the sprayed coatings was studied in order to overcome the drawbacks of sprayed structures and to markedly improve the coating properties. The coating material was high-chromium, nickel-chromium alloy, which contains small amounts of molybdenum and boron (53.3% Cr, 42.5% Ni, 2.5% Mo, 0.5% B). The coatings were prepared by HVOF spraying onto mild steel substrates. A high-power, fiber-coupled, continuous-wave Nd:YAG laser equipped with large beam optics was used to remelt the HVOF-sprayed coating using different levels of scanning speed and beam width (10 or 20 mm). Coating that was remelted with the highest traverse speed suffered from cracking because of the rapid solidification inherent to laser processing. However, after the appropriate laser parameters were chosen, nonporous, crack-free coatings with minimal dilution between coating and substrate were produced. Laser remelting resulted in the formation of a dense oxide layer on top of the coatings and full homogenization of the sprayed structure. The coatings as sprayed and after laser remelting were characterized by optical and electron microscopy (OM, SEM, respectively). Dilution between coating and substrate was studied with energy dispersive spectrometry (EDS). The properties of the laser-remelted coatings were directly compared with properties of as-sprayed HVOF coatings.     

不同参数下激光重熔Cr_3C_2-NiCr涂层冲蚀磨损性能研究

采用超音速火焰喷涂技术在低碳钢表而喷涂Cr_3C_2-NiCr涂层,然后在不同工艺参数下对其进行激光重熔处理.考察不同重熔参数下涂层的冲蚀性能.并与喷涂层对比.结果表明:在激光功率3.0 kW,扫描速率50mm/s的工艺参数下激光重熔.涂层的冲蚀失重最小.所形成的涂层表面均匀性较好;重熔层的致密度要优于喷涂层,重熔后涂层由机械结合转变为冶金结合;南于表面氧化层的存在和内部冶金结合的形成,重熔层硬度较喷涂层高.     

提高高速电弧喷涂再制造曲轴涂层结合强度的途径

分析了再制造发动机曲轴表面涂层结合强度低的原因,介绍了机器人自动化高速电弧喷涂技术、各种涂层重熔技术、高速电弧喷枪改进技术及复合梯度涂层材料设计在提高高速电弧喷涂再制造曲轴涂层结合强度中的应用。     

Corrosion properties of in situ laser remelted NiCrBSi coatings comparison with hard chromium coatings

This study aims at evaluating the effect of an in situ laser remelting treatment of NiCrBSi coatings, deposited by plasma spraying. Life Cycle Assessment (LCA) method was used to estimate the environmental impacts of coating processes. It was demonstrated with this LCA that the in situ remelting process was clean. Microstructural results were also evaluated. A good metallurgical bond was formed at the remelted coating interface. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. The dependence between the microstructure of NiCrBSi coatings, which was modified by laser treatment, and corrosion resistance has been evaluated by potentiodynamic polarization curves. Results show that, the corrosion resistance was increased because of a finer structure and higher densities of the coatings, but corrosion mechanisms occurring in all cases were different. From the electrochemical experiments in NaCl solution it can be deduced that laser remelting of as-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the disturbed structure of the as-sprayed samples, whereas the substrate surface of remelted coating is not reached, because of a higher density. But ClMO intermediate species were formed on the surface, because Cl⁻ can destroy the protective film on the coating. The hybrid plasma/laser process was cleaner than hard chromium plating and its corrosion behavior is superior too.     

TiAl合金表面激光重熔纳米陶瓷涂层

采用等离子喷涂和激光重熔复合工艺在TiA l合金表面制备了纳米A l2O3-13wt%TiO2复合陶瓷涂层。为了使重熔后的陶瓷涂层保留一定的纳米结构组织,采用相对较低的激光功率和能量密度进行重熔。用扫描电镜(SEM)和X射线衍射仪(XRD)分析了涂层形貌、微观结构和相组成。结果表明,等离子喷涂纳米陶瓷涂层由纳米颗粒完全熔化区和部分熔化区两部分组成,具有等离子喷涂态的典型层状结构;由于受到激光功率、能量密度、陶瓷材料热物性参数和涂层厚度等因素的综合影响,重熔后陶瓷涂层出现了明显的分层结构特征;依据组织形态的不同,可将其大致分为:重熔区、烧结区和残余等离子喷涂区。重熔区由致密细小的等轴晶组成,并且保留了部分来源于原等离子喷涂部分熔化区的残留纳米粒子。由于等离子喷涂过程中涂层沉积时的快速凝固作用,涂层以亚稳相-γA l2O3为主,经过激光重熔处理后,-γA l2O3又重新转变为稳定相-αA l2O3。     

冷喷涂Cu402F涂层激光重熔表面改性后摩擦学行为

目的研究激光重熔后冷喷涂Cu402F涂层在腐蚀介质中的摩擦学行为。方法采用冷喷涂技术在镍铝青铜9442合金上制备了厚度约为882.11μm的Cu402F涂层,并使用激光重熔技术对冷喷涂涂层进行表面改性。使用OM、SEM观察涂层截面与表面的微观形貌;使用XRD、X射线残余应力测试仪、多功能表面性能测试仪、多频直线往复磨蚀实验机,重点表征测试了涂层的组织、表面残余应力、摩擦学性能与磨蚀行为。结果激光重熔后的涂层分为表面重熔层、多孔的重熔过渡层以及冷喷涂遗传层。激光重熔前后,涂层的物相、残余应力均未发生较大变化。在20、50、100 N条件下,激光重熔态涂层的平均摩擦系数呈递增趋势,磨损率分别为1.01×10~(-2)、1.17×10~(-2)、1.34×10~(-2) mm~3/(N·m);由磨蚀实验可知,磨蚀是涂层表面产生钝化膜与钝化膜被破坏的此消彼长的过程,反映着摩擦与腐蚀的协同作用,涂层在磨蚀过程中,开路电位与摩擦系数呈正相关,说明激光重熔态涂层表面钝化膜产生的速度快于钝化膜被坏的速度。结论激光重熔保留了冷喷涂技术制备的Cu402F涂层的优点,同时激光重熔涂层上产生钝化膜的速度更快,有利于提高涂层的耐磨蚀性能。