Effect of Rare Earth on Microstructure of Vacuum Melting Ni-Based Self-Fluxing Alloy Coatings

The Ni-based self-fluxing alloy coating containing RE was acquired by the technique of vacuum melting on the hypoeutectoid steel (Fe-0.45%C) matrix. By X-ray diffraction, SEM and EDX, the microstructure and phase structure of section of coating and the microstructure near the interface between coating and matrix were investigated, and the effect of RE on microstructure of coating was also discussed. The results show that the microstructure of the NiCrBSi alloy coating is composed of Ni-based solid solution and a lot of massive, globular and needle secondary phases CrB, Ni_3B, Cr_7C_3, Cr_(23)C_6 among the solid solution. The metallurgical binding between steel matrix and coating is realized. RE makes needle phase of alloy coating vanish. New phases of NiB and Cr_(6.5)Ni_(2.5)Si are precipitated from alloy coating, and secondary phases of alloy coating are sphericized. Consequently, RE also hinders the diffusion of Ni, Cr and Si atoms from coating to matrix and Fe atoms from matrix to coating, holds back the dilution of Fe for NiCrBSi alloy coating, and assures the chemical composition of the alloy coating.

Effect of vacuum heat treatment on microstructure and microhardness of cold sprayed Cu-4Cr-2Nb alloy coating

The effect of vacuum heat treatment on the microstructure and microhardness of cold-sprayed Cu-4%Cr-2%Nb alloy coating was investigated. The heat treatment was conducted under the temperatures from 250 ℃ to 950 ℃ with a step of 100 ℃ for 2 h. It was found that a dense thick Cu-4Cr-2Nb coating could be formed by cold spraying. After heat treatment, a Cr2Nb phase was uniformly distributed in the matrix, which was transferred from the gas-atomized feedstock. A little grain growth of Cr2Nb phase was observed accompanying with the healing-up of the incomplete interfaces between the deposited particles at the elevated temperatures. The coating microhardness increases a little with increasing the temperature to 350 ℃, and then decreases with further increasing temperature up to 950 ℃. This fact can be attributed to the microstructure evolution during the heat treatment.

FORMATION OF GRADIENT COATING OF Fe-BASED ALLOY WITH RARE EARTHS BY PLASMA SURFACING

A gradient coating of Fe-based alloy was manufactured with rare earths (RE) by plasma surfacing on Q235 steel substrate. The coatings were studied by using X-ray diffraction(XRD), scanning electron microscope(SEM), differential thermal analyzer(DTA), and electron probe micro-analyzer (EPMA). The results show that the phases of the two kinds of coatings(with and without RE) both include α-Fe, Fe7C3, Fe3C, Cr2B, Fe2B and FeB. The microstructure of F314 coating is mainly hypereutectic, the pro-phases Cr7C3 and Cr2B are loose, crassi, spiculate and contain microcracks. The brittleness of the coating is high, and the average hardness is 787 HV. When 0.8wt% RE was added into the F314 alloy, the microstructure varied from hypoeutectic to hypereutectic continuously, The hardness appears as gradient distribution with the highest value of 773 HV, meanwhile, the brittleness decreases significantly. The formation of gradient structure depends on the fallowing factors: (i) the conversion of RE. The addition of RE lowers the elements point and Fe-C eutectic temperature, thus the base metal melting acutely. (ii) the heating of plasma arc. Graded temperature results in directional solidification, thus the gradient structure forms easily. The main reasons for the hardness decrease with RE addition in the alloy are the ratio of hard phase lowering and the hardness of the hard phase decreasing.

Effect of vacuum heat treatment on microstructure and corrosion behavior of HVOF sprayed AICoCrFeNiCu high entropy alloy

To improve the corrosion resistance of coalbed methane drilling equipment,an AICoCrFeNiCu high entropy alloy coating was prepared on the AISI 4135(35CrMo)steel substrate by high velocity oxygen fuel(HVOF)technology,and the coating was subjected to vacuum heat treatment(VHT)at different temperatures(500,700,900 and 1100℃).The corrosion test of the substrate and the coatings after VHT in coalbed methane drilling fluid was carried out.The results show that the HVOF sprayed AICoCrFeNiCu high entropy alloy(HEA)coating has a good bonding with the substrate,and the porosity of the coating is about 2.4%.There is partial segregation in the coating,and the coating mainly consists of body-centered cubic phase.The coating has good thermal stability,and the phase structure and microstructure of the coatings have changed after VHT at different temperatures.Compared with the substrate,the as-sprayed coating has better uniform corrosion resistance,and the corrosion resistance of the coating after VHT is further improved.After VHT at 500℃,the HVOF-sprayed AICoCrFeNiCu HEA coating has the best corrosion resistance.

Behavior of NiCrAlY coating on the TC6 titanium alloy

A NiCrAlY coating was deposited on the TC6 titanium substrate by arc ion plating （ALP）. The structure and morphologies of the NiCrAlY coating were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and the influence of vacuum heat treatment on the element diffusion behavior was studied. The results showed that the y＇-Ni3Al phase was precipitated on the NiCrAlY coating after heat treatment. The Ni3（AI,Ti）, TiNi, and Ti2Ni intermetallic layers appeared at the interface from the outside to the inside at 700℃, and the thickness of the intermetallic layers increased with the increase in temperature. At 700℃ Ti and Ni were the major diffusion elements, and the diffusion of Cr was observed when the heat treatment temperature increased up to 870℃. The violent inward diffusion of Ni at 950℃ resulted in the degradation of the NiCrAlY coating.

Influence of laser re-melting and vacuum heat treatment on plasma-sprayed FeCoCrNiAl alloy coatings

FeCoCrNiAl high entropy alloy coatings were prepared by supersonic air-plasma spraying.The coatings were post-treated by vacuum heat treatment at 600 and 900°C,and laser re-melting with 300 W,respectively,to study the influence of different treatments on the structure and properties of the coatings.The phase constitution,microstructure and microhardness of the coatings after treatments were investigated using X-ray diffraction,scanning electron microscopy and energy dispersive spectrometry.Results showed that the as-sprayed coatings consisted of pure metal and Fe-Cr.The AlNi;phase was obtained after the vacuum heat treatment process.A body-centered cubic structure with less AlNi;could be found in the coating after the laser re-melting process.The average hardness values of the as-sprayed coating and the coatings with two different temperature vacuum heat treatments and with laser re-melting were 177,227,266 and 682 HV,respectively.This suggests that the vacuum heat treatment promoted the alloying process of the coatings,and contributed to the enhancement of the coating wear resistance.The laser re-melted coating showed the best wear resistance.

Fe_(0.5)CrMnAlCu高熵合金及涂层的组织与性能

采用真空电弧熔炼与冷喷涂辅助感应重熔制备Fe_(0.5)CrMnAlCu高熵合金及涂层。利用XRD、SEM、显微硬度计、磨料磨损实验机对高熵合金及涂层的相结构、微观组织以及耐磨损等性能进行测试分析。结果表明:真空电弧熔炼制备的Fe_(0.5)CrMnAlCu高熵合金为FCC和BCC相固溶体结构,其组织形貌主要为枝晶和枝晶间组织,冷喷涂辅助感应重熔合成Fe_(0.5)CrMnAlCu高熵合金涂层的相结构为单一的BCC结构,其组织形貌为枝晶和枝晶间组织。由于感应重熔合成Fe_(0.5)CrMnAlCu高熵合金涂层较电弧熔炼制备的高熵合金具有更大的晶粒尺寸,同时涂层的原子尺寸差δ大于合金的原子尺寸差,导致感应重熔合成Fe_(0.5)CrMnAlCu高熵合金涂层的硬度是真空电弧熔炼高熵合金的1.37倍,其磨损率比真空电弧熔炼制备的高熵合金磨损率降低18%。真空电弧熔炼与冷喷涂辅助感应重熔制备Fe_(0.5)CrMnAlCu高熵合金及涂层的磨损机制主要是黏着磨损、磨粒磨损。

热轧温度对Ti-Zr-V-Nb-Si合金微观组织和力学性能的影响

采用真空电弧熔炼制备了密度仅为6.1 g/cm^(3)的(TiZrV_(0.5)Nb_(0.5))_(99.4)Si_(0.6)轻质高熵合金,并分别选取900℃、1000℃和1100℃的热轧温度对合金进行轧制改性处理,探究了不同热轧温度对微观组织与力学性能的影响。结果表明:真空电弧熔炼制备的合金经轧制后强度和延伸率均得到提高,在900℃下热轧的合金具有的1164.5 MPa的拉伸断裂强度以及14.7%的延伸率,性能提升最佳,较铸态合金分别提高了13.9%和950%。随着热轧温度的进一步升高,合金平均晶粒尺寸变大、力学性能不断下降。900℃下热轧后合金优异的综合力学性能是位错增殖、固溶强化、第二相强化和晶粒细化四种强化机制共同作用的结果。

DZ125合金表面激光熔化沉积Tribaloy T-800/WC复合涂层的显微组织和力学性能

目的提高锯齿冠的表面耐磨性能,延长涡轮叶片的使用寿命。方法采用激光熔化沉积技术在DZ125合金表面制备T-800合金涂层和T-800/WC(5%)复合涂层,重点分析涂层的宏观形貌、物相组成、显微组织、硬度以及摩擦磨损性能。结果T-800合金涂层和T-800/WC复合涂层内部均不存在裂纹。与T-800合金涂层相比,T-800/WC复合涂层的高度增加,稀释率降低。T-800合金涂层物相主要包括面心立方结构Co相和Laves相(Co3Mo2Si),T-800/WC复合涂层中额外存在WC相、W2C相、Co6Mo6C相。T-800合金涂层和T-800/WC复合涂层的组织主要为平面晶、“花状”Laves相、粗大Laves相以及共晶组织。T-800合金涂层的平均显微硬度和摩擦因数分别为630HV0.5、0.42,WC的加入使得涂层性能得到提升,T-800/WC复合涂层的平均显微硬度和摩擦因数分别为697HV0.5、0.37。添加WC后,T-800合金涂层磨损机理由磨粒磨损、黏着磨损和氧化磨损转变为磨粒磨损、疲劳磨损和氧化磨损。结论WC的添加促进了涂层晶粒细化和Laves相的析出,使得涂层的硬度和耐磨性得到提升。

FeCrMnAl_(x)Cu_(_((2-x)))高熵合金的组织与性能

采用真空电弧熔炼技术制备了FeCrMnAl_(x)Cu_((2-x))(x=1.3,1.4,1.5,1.6,1.7)高熵合金,研究了Al、Cu含量对FeCrMnAl_(x)Cu_((2-x))高熵合金组织结构、力学性能和摩擦学性能的影响.结果表明:FeCrMnAl_(x)Cu_((2-x))高熵合金为BCC结构单相固溶体.组织均由树枝晶组成,随x的增加,屈服强度逐渐上升,在x=1.5时,达到最大值1092.31 MPa.抗压强度和变形率均随x的增加呈下降趋势,且在x=1.3时达到最大值,分别为1517.84 MPa和43.36%.FeCrMnAl_(1.7)Cu_(0.3)高熵合金显微硬度达到最大值559.9 HV.磨损率最小为4.70×10^(-6)mm^(3)N^(-1)m^(-1).随x的增大,合金磨损机制主要以磨粒磨损、粘着磨损、氧化磨损为主.

真空熔结镍基合金涂层的组织结构及其高温磨损特性

研究了一种真空熔结镍基合金涂层的组织结构及其干摩擦滑动磨损特性。结果表明,镍基合金涂层中的析出相主要有硼化物、碳化物和硅化物,其中硼化物、碳化物起强化作用,硅化物改善涂层熔结过程中的工艺性能。涂层磨损的主要方式是微犁削,因镍基合金涂层具有较高的高温硬度,高温下具有良好的抗磨性能。磨损过程中在磨损表面覆盖的氧化物层对涂层起到保护和减磨作用。

NiCrAlY涂层/TC4基体界面反应机理

采用电弧离子镀技术在TC4(Ti6Al4V)合金基体表面沉积制备NiCrAlY涂层。通过扫描电镜与能谱分析、X射线衍射分析及显微硬度测试,研究真空热处理对NiCrAlY涂层组织性能的影响;分析界面反应产物的形成过程;讨论Cr元素在界面反应中的作用机制。研究结果表明:真空热处理后NiCrAlY涂层中有γ-′Ni3Al相析出,提高了涂层的表面硬度;在870℃以下热处理,NiCrAlY涂层/TC4基体界面反应产物的出现顺序依次为:相变影响区→Ni3(Al,Ti)和Ti2Ni化合物层→TiNi化合层;Cr元素在870℃以上开始扩散并参与界面反应,形成TiCr2化合物。

真空熔结铁基合金涂层的组织结构分析

分析了一种新型真空熔结铁基合金涂层的组织结构。铁基合金涂层是以高铬铸铁为粘结相、以大颗粒 (Cr,Fe) 2 (C ,B)相为硬质相的复合材料 ;(Cr,Fe) 2 (C ,B)相的体积分数约80 % ,粘结相是以奥氏体为基体、其中分布有针状 (Cr ,Fe) (C ,B)相、针状 (Cr ,Fe) 7C3 相和粒状 (Cr ,Fe) 7C3 相。铁基合金涂层的洛氏硬度为HRC5 5 ,表面洛氏硬度为HRA5 7。

薄带钎料真空熔结制备CoCrW耐磨涂层

采用薄带钎料粘贴在CoCrW预置层表面进行真空加热,实现了真空熔结制备涂层的新方法,对涂层的组织和抗微动磨损性能进行了研究。结果表明:涂层组织致密,涂层与基体和Ni基钎料与CoCrW粉末颗粒之间能够形成良好的冶金结合。熔结涂层组织由Co基和Ni基固溶体以及Co_6W_6C,Cr_7C_3,W_2C,Ni_3B,CrB等硬质相组成。基于致密的组织、良好的冶金结合和综合力学性能,真空熔结CoCrW涂层显示出优秀的抗微动磨损性能。

炉熔处理对等离子喷涂Ni基WC型自熔合金涂层组织形态的影响

研究了等离子喷涂Ni基WC型自熔合金涂层炉熔处理前后的组织形态。结果表明 ,经重熔处理后 ,涂层由富含孔隙、未熔颗粒的层状结构转变为致密的结晶组织结构 ,涂层与基材由机械咬合结合转变为冶金反应扩散结合 ,涂层的内聚强度和涂层 /基材的结合强度都得以显著改善。涂层的相组成在重熔前后变化不大 ,均主要由γ Ni固溶体相 ,Ni B(Ni2 B) ,Cr B(CrB) ,Ni Si(Ni5Si2 )和WC硬质相等组成。由于等离子喷涂是一种快速凝固工艺 ,在喷涂态涂层中形成了部分非晶相 ,经重熔处理后 ,非晶相发生完全晶化。

Nb对激光熔覆MoFeCrTiWAlNb_x高熔点高熵合金组织与性能的影响

为了获得高性能的涂层材料,采用激光熔覆技术,在W_6Mo_5Cr_4V_2AlA工具钢表面制备MoFeCrTiWAlNb_x(x=1,1.5,2,2.5,3)高熔点高熵合金涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、硬度计和摩擦磨损试验机等测试手段,研究了Nb对激光熔覆MoFeCrTiWAlNb_x高熵合金涂层组织与性能的影响。结果表明,涂层主要由BCC相、MC相和少量拉弗斯相组成,包括先共晶组织和共晶组织。随着Nb含量的增加,先共晶碳化物数量减少、尺寸增加,呈现不规则颗粒状变化。共晶组织的体积分数逐渐增大,共晶组织中BCC相逐渐增多而(MC)_e相逐渐减少,共晶组织形貌也逐渐由不规则块状小颗粒+棒状枝晶变为大块状颗粒+网状枝晶;涂层硬度逐渐下降,耐磨性逐渐上升,涂层磨损机理以粘着磨损、磨粒磨损为主。

熔炼方式对TC17钛合金铸锭化学成分及棒材组织均匀性的影响研究

对比分析一次电子束冷床炉熔炼(EBCHM)加一次真空自耗电弧炉熔炼(VAR)和三次真空自耗电弧炉熔炼生产的φ820 mm TC17钛合金铸锭的化学成分均匀性,以及由这两种铸锭经相同工艺锻造得到的棒材的组织均匀性。结果表明,通过原材料控制和工艺参数设计,两种熔炼方式均可生产出化学成分均匀、杂质含量可控的大规格TC17钛合金铸锭,且EBCHM+VAR工艺在残钛回收方面具有优势;两种工艺得到的铸锭,经相同的锻造工艺可获得组织均匀的棒材,为航空转动件提供材料支撑。

钇和铈对AZ91D镁合金的组织及力学性能的影响

采用真空熔炼金属型铸造方法,在AZ91D镁合金中添加适量的稀土元素钇和铈,研究钇和铈对AZ91D组织和力学性能的影响规律。结果表明,在AZ91D中添加适量钇和铈可以使合金的组织细化,Mg17Al12第二相分布均匀弥散,提高AZ91D镁合金的力学性能。

真空雾化CoCrAlTaY热喷涂粉末的特性及其涂层的结合强度

采用真空雾化制备了CoCrAlTaY高温合金粉末。结果表明:该合金粉末呈球形,粉末粒度呈近正态分布,粉末由CoAl、γ、Cr27C3和TaC相组成;合金粉末涂层与基体结合良好,其结合力达到52 MPa。

高温合金表面激光熔铸镍基合金涂层的组织与耐磨性能

研究了高温合金ＧＨ３３表面激光熔铸镍基合金涂层的组织和耐磨性能。结果表明，基材对涂层合金的稀释作用较小；涂层与基材之间形成良好的冶金接合；涂层基体组织为γ－Ｎｉ枝晶，枝晶间为γ－Ｎｉ、Ｍ２３（ＣＢ）６、Ｎｉ３Ｂ、Ｃｒ２Ｂ、ＣｒＢ、ＷＣ等；涂层耐磨性能的平均值较基材提高４倍以上。