铝材表面激光熔覆Ni_(1.5)Co_(1.5)FeCrTi_x高熵合金层的组织与性能

为了提高铝合金的耐磨性及耐蚀性并降低高熵合金中元素偏析的现象,采用CO_2激光熔覆技术在铝基体表面制备了Ni_(1.5)Co_(1.5)FeCrTi_x高熵合金熔覆层。借助光学显微镜、扫描电镜、X射线衍射仪和电化学工作站检测技术研究了Ti含量对Ni_(1.5)Co_(1.5)FeCrTi_x熔覆层显微组织和耐蚀性能的影响。结果表明:Ni_(1.5)Co_(1.5)FeCrTi_x高熵合金熔覆层主要相结构为简单的面心立方相、金属间化合物相和Laves相;当Ti含量摩尔比从0.5增至2.0时,Ni_(1.5)Co_(1.5)FeCrTi_x高熵合金熔覆层的表面硬度从510 HV增加到554 HV,在0.5 mol/L HNO_3溶液中具有优异的耐蚀性能。     

WC和Nb对氩弧熔覆Ni60+WC+Nb合金层组织和耐磨性的影响

采用氩弧熔覆工艺在4Cr13钢上分别熔覆Ni60、Ni60+WC和Ni60+WC+Nb系合金。比较各种材料熔覆层的显微组织、显微硬度和耐磨性。结果表明,材料的表面硬度和耐磨性等都随WC含量的增加得到很大地提高,而Nb含量的增加对硬度和耐磨性的影响不明显。     

热轧45钢表面Ni60-WC涂层的高频感应熔覆及其电接触强化前后的性能

为了降低WC增强镍基合涂层的制备成本,提高其表面性能,采用高频感应熔覆技术在热轧45钢表面制备Ni60-WC合金层,并对熔覆层进行电接触强化。采用光学显微镜、X射线衍射仪及显微硬度计分析了熔覆层电接触强化前后的形貌、相结构及显微硬度;采用滚动疲劳接触磨损试验研究了熔覆层电接触强化前后的耐磨性。结果表明:热轧态45钢感应熔覆层组织较为致密,但存在孔洞、夹生缺陷;熔覆层电接触强化后组织更加致密,孔洞减少,夹生层重新熔合,热影响区减小;熔覆层电接触强化前后的相结构相同,均由WC,W2C,Cr23C6,Cr7C3,Fe Ni,Ni3Fe等相组成;熔覆层电接触强化后的显微硬度和耐磨性较电接触强化前大幅提高,熔覆层电接触强化后抗疲劳磨损性能大幅提高且远高于淬火态45钢的。     

Ti6Al4V合金激光熔覆γ-NiCrAlTi/TiC复合层的组织与摩擦学性能

为提高Ti6Al4V合金的摩擦学性能,以NiCr-Cr₃C₂金属陶瓷粉末为涂覆材料,采用激光熔覆技术在Ti6Al4V表面制备以TiC为增强相、γ-NiCrAlTi固溶体为增韧相的熔覆层。采用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱仪（EDS）分析了熔覆层的物相组成及显微组织,测试了熔覆层沿层深方向的硬度分布,分别在室温（24℃）,300,600℃测试了熔覆层和Ti6Al4V合金基体的干滑动磨损性能。结果表明:熔覆层的平均硬度约1 100HV_{2 N},约为基体的3倍;室温时,由于高硬度增强相TiC和增韧相γ-NiCrAlTi固溶体的综合效应,激光熔覆γ-NiCrAlTi/TiC复合层的摩擦系数和磨损率比Ti6Al4V合金基体的显著降低,熔覆层具有较好的耐磨减摩性能,磨损机理主要为黏着磨损;300,600℃时,熔覆层被氧化,耐磨性减弱,磨损机理主要为黏着磨损和塑性变形。     

CoCrFeNiTix高熵合金涂层的显微组织和耐磨性能

用激光熔覆工艺在40Cr钢表面制备CoCrFeNiTi_x (x=0、0.2、0.5、0.8)高熵合金涂层并计算其热力学参数,使用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)、显微硬度仪、摩擦磨损试验机等手段检测合金的物相组成、组织、元素分布、硬度及耐磨性,研究了Ti元素含量对其显微组织和耐磨性能的影响。结果表明：随着Ti元素含量的提高,合金物相在面心立方(FCC)结构的基础上形成了体心立方(BCC)结构,熔覆层中部的组织由晶界明显、晶粒分布均匀的等轴晶组成,最后形成了柱状树枝晶;随着Ti元素含量的提高,合金横截面的硬度逐渐提高,最高为412.32 HV_0.2,比基体的硬度提高了1.8倍;涂层的磨损量和摩擦系数均随之降低,Ti含量为0.8时涂层其耐磨性能最优,磨损量最小为6.8 mg,摩擦系数为0.35。涂层的磨损机制,以磨粒磨损、粘着磨损和氧化磨损为主。     

45钢表面激光熔覆CoCrNi中熵合金涂层组织与性能

为探究CoCrNi中熵合金在激光熔覆领域中的应用,以CoCrNi合金粉末作为熔覆粉末,在45钢表面采用同轴送粉法制备合金涂层。利用扫描电镜、X射线衍射仪、显微硬度仪、摩擦磨损实验机和电化学工作站等设备研究了熔覆层微观组织、硬度、耐磨性和耐腐蚀性能。结果表明：熔覆层成形良好,组织均匀致密,组成相主要为FCC单相固溶体;熔池与基体交界处为平面晶,底部靠近中心为柱状晶,顶部分别为胞状晶和等轴晶,3种元素在熔覆层深度方向上的比例几乎相同;熔覆层平均硬度为250HV,摩擦系数、磨损量较基体分别降低了11.7%和36.7%;自腐蚀电流密度略有降低,CoCrNi熔覆层的钝化区域为-150到1 100 mV,表明熔覆层显著提高45钢的耐腐蚀性能。     

等离子熔覆法制备AlxCoCrFeNi高熵合金微观组织与性能研究

利用等离子熔覆法在Q235基体上制备了Al_xCoCrFeNi(x=1、1.5,x为摩尔分数)高熵合金,对熔覆层的化学成分、相结构、微观组织和显微硬度进行了研究。结果表明:熔覆态高熵合金具有简单的固溶体结构,微观组织为树枝晶,Al含量从x=1增加到x=1.5时,物相组成由FCC+BCC两相转变为单一的BCC相;当x=1.5时,枝晶间有纳米级颗粒析出;Al_(1.5)CoCrFeNi熔覆层与基体呈现良好的冶金结合,界面附近的热影响区由于珠光体脱碳分解而形成了约为80μm宽的铁素体带;随着Al含量的增加,熔覆层的显微硬度从x=1时的478HV增加到x=1.5时的530HV。     

Si含量对氩弧熔覆AlCuFeNiCoSix高熵合金涂层组织及性能的影响

高熵合金具有独特的相结构和优异的性能。采用氩弧熔覆技术在Q235钢上制备AlCuFeNiCoSi_x高熵合金涂层,探究Si对AlCuFeNiCo高熵合金涂层组织、硬度与耐磨性的影响。结果得出：高熵合金涂层仅由BCC和FCC相结构组成,并没有复杂相出现,随Si含量增加,BCC结构衍射峰强度先减小再增加,组织主要为树枝晶组织,随Si含量增加,枝晶组织先变成棒状枝晶,然后又变成细小致密且不均匀。涂层硬度先减小后增大,然后又减小,当x=0.75时硬度最高,达到62.5 HRC。加入Si含量0.75的涂层耐磨性比未加入Si涂层的提高了26.3%。     

Q345钢激光熔覆镍基WC合金的组织与耐磨性能

为进一步提高Q345钢激光熔覆层的耐磨性能,利用激光熔覆技术在Q345钢表面制备了70%Ni60A+30%WC熔覆层(质量分数)。采用X射线衍射仪及扫描电镜分析了熔覆层的物相、显微组织,采用摩擦磨损试验研究其耐磨性能。结果表明,Q345钢表面激光熔覆镍基WC合金对其表面的晶粒细化、显微硬度和耐磨性等都有很大提升。     

钢表面颗粒增强熔覆层的组织和性能

采用预置法在45号钢表面制备WC颗粒增强熔覆层,研究了熔覆层的组织和性能,并与淬火态Cr12MoV(59HRC)的耐磨性能进行比较,分析磨损机理并讨论WC颗粒的磨损现象。结果表明:熔覆层与基材之间结合良好并形成界面反应层;熔覆层组织分布均匀,表面弥散分布着大量WC颗粒;熔覆层的平均硬度比基材的高,耐磨性是基材45号钢的18倍,是淬火态Cr12MoV的2倍;在磨损实验中熔覆层的增强颗粒WC出现罕见的表面磨平和脆性脱落现象。     

Microstructure and properties of laser-clad FeNiCoCrTi0.5Nb0.5 high-entropy alloy coating

ABSTRACT

FeNiCoCrTi_0.5Nb_0.5 high-entropy alloy coating is prepared on AISI 1045 steel by laser cladding. The cross-sectional macroscopic morphology, phase, microstructure, microhardness and wear resistance are studied systematically. The results show that FeNiCoCrTi_0.5Nb_0.5 coating has no porosities, cracks or other defects and is well metallurgically bonded to the substrate. The coating is composed of body-centred cubic (BCC) solid solution, face-centred cubic (FCC) solid solution and hard Laves phase. The solid solution phase and Laves phase distribute uniformly and closely in a lamellar shape to form a fine and dense eutectic structure. The microhardness of FeNiCoCrTi_0.5Nb_0.5 coating is about three times that of the substrate. Compared with the substrate, the coating has superior wear resistance.     

Development of novel CoCu0.5FeNiVTix (x = 0, 0.5, 1, 1.5, 2) high-entropy alloys

CoCu_0.5FeNiVTi_x (x?=?0, 0.5, 1, 1.5, 2) high-entropy alloys (HEAs) were prepared using vacuum arc melting. The microstructures, crystal structures, hardness, compressive properties and wear resistances of the alloys were studied. The alloys always contained face-centred cubic (FCC) and body-centred cubic (BCC) solid solution regardless of the increase in Ti content. The microstructure of alloys exhibited typical dendritic characteristics, which were more and more unapparent with the increase in the Ti content. The alloys with a high content of Ti had a high compressive strength and low ductility. Owing to the formation of nano-precipitates and BCC as the major phase, the CoCu_0.5FeNiVTi₁ alloy exhibited the highest compressive strength of 2747?MPa and a plastic strain limit of 7.4%. As the content of Ti was increased, the wear resistance of CoCu_0.5FeNiVTi_x alloys displayed a rapid increase and reached the highest value when x?=?1, and finally decreased. Because of the large volume fraction of BCC, the CoCu_0.5FeNiVTi₁ alloy exhibited high hardness so exhibiting the best wear resistance. Adhesive wear and abrasive wear dominated the wear behaviour of CoCu_0.5FeNiVTi_x alloys during sliding against SUJ2 steel.     

Microstructures and mechanical properties of Nb-alloyed CoCrCuFeNi high-entropy alloys

Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys (HEAs) with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the (CoCrCuFeNi)_100-xNb_x HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC (face-centered cubic) to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases. Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of (CoCrCuFeNi)_100-xNb_x HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% (no fracture) to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC (valence electron concentration) value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.     

W6Mo5Cr4V2高速钢WC/Co激光熔覆表面的摩擦磨损性能

为了改善高速钢表面的摩擦磨损性能,应用激光熔覆技术在W6Mo5Cr4V2高速钢表面制备出WC/Co熔覆道。采用三维数码显微镜观察熔覆试件的金相组织并借助显微硬度计测试其显微硬度。采用销盘式摩擦磨损试验机分别对高速钢和WC/Co熔覆试件进行了摩擦磨损试验,并采用三维数码显微镜观察磨损形貌。结果表明:与高速钢基材相比,WC/Co熔覆道硬度提高,熔覆试件的摩擦系数和磨损量降低;WC/Co熔覆道的磨损机制以磨粒磨损为主,熔覆道间隔以磨粒磨损和黏着磨损为主;熔覆道的硬度提高、减摩效果、散热作用以及试件表面熔覆道与间隔面的软硬交替,有助于提高WC/Co熔覆试件的摩擦磨损性能。     

Effect of Niobium on Microstructure and Properties of the CoCrFeNb_xNi High Entropy Alloys

A series of CoCrFeNb_xNi(x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2) high entropy alloys(HEAs) was prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. The results indicate that the prepared CoCrFeNb_xNi(x 0) HEAs consist of a simple FCC solid solution phase and a Laves phase. The microstructures of the alloys change from an initial single-phase FCC solid solution structure(x = 0) to a hypoeutectic microstructure(x = 0.25), then to a full eutectic microstructure(x = 0.45) and finally to a hypereutectic microstructure(0.5 x 1.2). The compressive test results show that the Nb0.45(x = 0.45) alloy with a full eutectic microstructure possesses the highest compressive fracture strength of 2558 MPa and a fracture strain of 27.9%. The CoCrFeNi alloy exhibits an excellent compressive ductility, which can reach 50% height reduction without fracture. The Nb0.25 alloy with a hypoeutectic structure exhibits a larger plastic strain of 34.8%. With the increase of Nb content, increased hard/brittle Laves phase leads to a decrease of the plasticity and increases of the Vickers hardness and the wear resistance. The wear mass loss, width and depth of wear scar of the Nb1.2(x = 1.2) alloy with a hypereutectic structure are the lowest among all alloy systems, indicating that the wear resistance of the Nb1.2 alloy is the best one.     

Growth rate of Nb<Subscript>3</Subscript>Sn for reactive diffusion between Nb and Cu–9.3Sn–0.3Ti alloy

In order to examine experimentally the growth behavior of Nb₃Sn during reactive diffusion between Nb and a bronze with the α + β two-phase microstructure, a sandwich (Cu–Sn–Ti)/Nb/(Cu–Sn–Ti) diffusion couple was prepared from pure Nb and a ternary Cu–Sn–Ti alloy with concentrations of 9.3 at.% Sn and 0.3 at.% Ti by a diffusion bonding technique. Here, α is the primary solid-solution phase of Cu with the face-centered cubic structure, and β is the intermediate phase with the body-centered cubic structure. The diffusion couple was isothermally annealed at temperatures between T = 923 and 1,053 K for various times up to 843 h. Owing to annealing, the Nb₃Sn layer is formed along each (Cu–Sn–Ti)/Nb interface in the diffusion couple, and grows mainly into Nb. Hence, the migration of the Nb₃Sn/Nb interface governs the growth of the Nb₃Sn layer. The mean thickness of the Nb₃Sn layer is proportional to a power function of the annealing time. The exponent of the power function is close to unity at T = 923 K, but takes values of 0.8–0.7 at T = 973–1,053 K. Consequently, the interface reaction at the migrating Nb₃Sn/Nb interface is the rate-controlling process for the growth of the Nb₃Sn layer at T = 923 K, and the interdiffusion across the Nb₃Sn layer as well as the interface reaction contributes to the rate-controlling process at T = 973–1,053 K. Except the effect of Ti, the growth rate of the Nb₃Sn layer is predominantly determined by the activity of Sn in the bronze and thus the concentration of Sn in the α phase. As a result, the growth rate is hardly affected by the volume fraction of the β phase, though the final amount of the Nb₃Sn layer may depend on the volume fraction.     

激光熔覆镍基合金层的组织与高温耐磨性能

为了改善304不锈钢工件的高温耐磨性能,利用CO2激光器在其表面熔覆了Ni基高温合金层。研究了熔覆层的物相组成、显微组织、成分分布,测试了其显微硬度、高温耐磨性能等,并与基材进行了对比。结果表明:Ni基合金熔覆层的组织从熔池底部到表层为胞状晶—柱状枝晶—树枝晶;熔覆层的主要组成相是Ni3Cr2,NbC,Mo2C与Cr23C6;Ni基合金粉末中添加难熔元素Cr,Mo,Nb等对熔覆层的组织起到了固溶强化、硬质相强化和弥散强化作用;熔覆层的平均显微硬度达到了405 HV,高温耐磨性能是基体的2倍多。