磁控等离子弧堆焊过程中热力学特点初探

在铁基合金的等离子堆焊过程中,施加水冷和磁场. 通过调整水冷和磁场状态进行堆焊试验,并对堆焊试样的显微组织进行分析,探究磁控状态下铁基堆焊层的相变热力学特点. 结果表明,外加磁场和强制水冷可以改变堆焊层中硬质相的分布和形态,外加磁场通过降低奥氏体相变势垒,使相变驱动力增大,临界形核半径减小,进而提高硬质相的形核率. Cr₇C₃硬质相的易磁化轴与其择优生长方向一致,均为“长条形”侧面.     

冲蚀角对超音速火焰喷涂Cr3C2-NiCr涂层冲蚀磨损行为的影响

采用超音速火焰喷涂(high-velocity oxygen-fuel, HVOF)技术,在1Cr18Ni9Ti不锈钢表面制备Cr₃C₂-NiCr金属陶瓷复合涂层. 研究了涂层的显微组织、相组成以及涂层和不锈钢的冲蚀行为和机理,探讨了冲蚀角与耐冲蚀性能的关系规律. 结果表明,涂层组织结构致密均匀,主要由Cr₃C₂以及少量的Cr₇C₃, Cr₂₃C₆和(Ni, Cr)固溶体相组成. Cr₃C₂-NiCr涂层的耐冲蚀性能随着冲蚀角的增大而减小,在低冲蚀角下涂层的破坏形式主要为微切削,重量损失较低,表现出优异的耐冲蚀性能. 随着冲蚀角的增大,冲蚀沙粒对涂层产生垂直冲击作用,粘结相与硬质相之间产生裂纹导致粘结相脱落,硬质相失去粘结相的支撑作用而裸露出来,在冲蚀沙粒的持续攻击下剥落,形成许多小冲蚀坑. 随着剥落硬质相数量的增加,小冲蚀坑逐步发展为大冲蚀坑,重量损失较大,耐冲蚀性能较差.     

M7C3的形态分布对铁基复合层耐磨性能的影响

研究了在电磁搅拌的作用下,硬质相M7C3(主要是(Fe, Cr)7C3和Cr7C3)的数量和形态分布对堆焊层金属耐磨性的影响规律.对堆焊试件进行耐磨、硬度试验,并采用SEM,XRD对堆焊进行显微组织和成分分析.发现随着磁场参数的改变,硬质相M7C3由杂乱无章的分布逐渐转变为较规则的六方块状分布,堆焊层金属的耐磨性也随之增强;当磁场电流为3A,磁场频率为10Hz时,堆焊层金属的性能达到最佳状态,此时堆焊层中硬质相(M7C3)均成较规则的六方块状分布.结果表明,在适当的磁场参数作用下,硬质相(M7C3)成较规则的六方块状分布可以显著的提高堆焊层金属的耐磨性.     

WxC增强镍基合金等离子堆焊层组织与空蚀性能

采用等离子堆焊技术在316L不锈钢表面原位合成W_xC增强镍基复合材料涂层,对涂层显微组织、相组成、硬质增强相的分布、显微硬度以及空蚀性能进行了分析.结果表明,Colmonoy 88合金等离子堆焊成形性良好,组织致密;堆焊层组织主要由γ-Ni固溶体,原位合成多角形、颗粒状W_xC及少量的Cr₇C₃,Fe₃W₃C,CrB₂相组成.堆焊过程中,熔池温度低于1 655 K时,原位生成WC和W₂C,温度高于1 655 K时,原位生成的WC发生了分解.镍基合金堆焊层平均硬度可达1 619 HV,为基材的8倍以上,在3.5% NaCl溶液中镍基复合材料抗空蚀性能为316L不锈钢基材的5倍.     

Fe-Cr-Ti-C系药芯焊丝熔覆层中硬质相生长模式

将Fe-Cr-Ti-C系耐磨药芯焊丝采用钨极氩弧焊堆焊到低碳钢表面,分析熔覆层中的物相组成,研究熔覆层中硬质相的形态分布和生长机理,探究熔覆层的耐磨性及表面硬度等力学性能变化的原因. 结果表明,药芯堆焊焊丝中的合金元素的过渡系数很高,可原位合成(Fe,Cr)₇C₃和TiC硬质相,TiC优先依附外来界面行核、长大,共晶(Fe,Cr)₇C₃硬质相则依附于初生马氏体相和TiC形核生长,点状TiC硬质相(少数为条状和十字状)弥散分布于马氏体、残余奥氏体的基体中,与网状的(Fe,Cr)₇C₃耐磨框架组成复合硬质相,提高熔覆层的耐磨性.     

等离子喷涂WC-20Cr3C2-7Ni/8YSZ复合涂层的组织及摩擦学性能

为提高连铸机拉矫辊的服役寿命,通过等离子喷涂技术在模具钢H13表面制备不同质量比的WC-20Cr₃C₂-7Ni+8YSZ复合涂层,分析各涂层的微区组织、显微硬度、抗划伤性、耐磨性和磨损形式。结果表明,在WC-20Cr₃C₂-7Ni粉末中分别加入30wt%、50wt%的8YSZ,其复合涂层的致密性明显提高,且涂层晶粒明显得到细化;WC-20Cr₃C₂-7Ni涂层中出现WC_1-x与W相,且随着8YSZ的添加WC相的结晶强度变弱;WC-20Cr₃C₂-7Ni+30wt%8YSZ涂层平均硬度(1172 HV0.2)相对于WC-20Cr₃C₂-7Ni涂层(1152 HV0.2)并没有明显变化,WC-20Cr₃C₂-7Ni+50wt%8YSZ涂层硬度(1052 HV0.2)相对于WC-20Cr₃...     

激光熔覆Fe/NiCr-Cr3C2复合涂层的组织和磨损性能

利用激光熔覆技术在GCr15 钢表面制备Fe/NiCr-Cr₃C₂复合涂层,研究不同NiCr-Cr₃C₂含量对铁基涂层微观组织和磨损性能的影响。结果表明:随NiCr-Cr₃C₂含量的增多,复合涂层显微组织逐渐细化,在铁基合金里掺入NiCr-Cr₃C₂金属陶瓷粉末导致复合涂层里残留奥氏体含量增多,α-Fe相含量减少,截面硬度显著降低。当加入10%NiCr-Cr₃C₂时,复合涂层中出现较多的Cr₃C₂和Cr₂₃C₆硬质相,同时磨痕表面生成了具有减摩作用的氧化产物,从而降低了磨耗和摩擦阻力,使涂层表现出最佳的耐磨性能。     

TiN对Fe-Cr-C耐磨堆焊合金组织及耐磨性影响

通过药芯焊丝的方式制备Fe-Cr-C-Ti-N和Fe-Cr-C堆焊层，讨论堆焊层中TiN对堆焊层耐磨性能和显微组织的影响. 利用洛氏硬度计检测堆焊层的宏观硬度，通过湿砂轮磨损试验机对堆焊层进行磨料磨损试验，利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析仪(EDS)、透射电子显微镜(TEM)等设备进行检测分析. 结果表明，含有TiN的堆焊层中，初生M₇C₃明显比不含TiN的组织细小，并且堆焊层硬度和耐磨性也相应提高. 通过热力学计算得出，熔池冷却过程中TiN先于M₇C₃析出. 由动力学计算可知TiN/M₇C₃的二维错配度为8.43%，TiN可做为初生M₇C₃的异质形核质点，使M₇C₃晶粒细化.     

Cr3C2/VC复合抑制剂比例对WC-10%Co超细晶硬质合金微观结构和力学性能的影响

本文以WC-10%Co为研究对象，添加质量分数1.0%的Cr₃C₂/VC复合抑制剂，在1 410℃下烧结1 h，制备了WC-10%Co-Cr₃C₂/VC超细晶硬质合金，研究了Cr₃C₂/VC复合抑制剂比例对物相组成、WC晶粒尺寸和粒度分布、WC三维形貌及力学性能的影响。结果表明：随Cr₃C₂含量的减少和VC含量的增加，WC平均晶粒尺寸先快速后缓慢减小，WC粒度分布不断变窄；WC形貌由三棱柱向台阶三棱柱转变，WC(0001)晶面上的台阶数量不断增加，这些台阶会显著降低合金的断裂韧性和抗弯强度；WC-10%CoCr₃C₂/VC超细晶硬质合金的硬度先快速后缓慢增加，而断裂韧性和抗弯强度先快速后缓慢降低；当w(Cr₃C₂)∶w(VC)=4∶1时，WC-10%Co-0.8%Cr₃C₂-0.2%...     

激光熔覆Ni-WC/Cr3C2涂层组织及性能

采用激光技术在45钢表面熔覆Ni-WC/Cr₃C₂涂层,采用SEM,XRD等手段进行熔覆层的显微组织、相组成及成分分析,并测试熔覆层的耐蚀性和耐磨性能.结果表明,Ni-WC/Cr₃C₂熔覆层底部生成方向性较强的胞状树枝晶,中上部组织为细小的树枝晶.涂层主要是由γ-(Fe, Ni),M₂₃C₆型碳化物以及未熔的WC颗粒组成.细晶强化、合金元素固溶强化以及碳化物强化的共同作用,使熔覆层的显微硬度提高至711HV0.1.熔覆层耐蚀性明显改善,腐蚀电流密度约为45钢的1/4.随着摩擦速度的增大,激光熔覆Ni-WC/Cr₃C₂涂层和45钢磨损量增加,且熔覆层的磨损量低于45钢,表明其耐磨性能明显提高.     

原位合成TiC和M7C3陶瓷硬质相的生长习性

采用等离子弧堆焊设备在低碳钢表面堆焊一层Fe—Cr-Ti—C系陶瓷复合堆焊合金,原位合成TiC和M7C3陶瓷硬质相,分析熔池中TiC和M7C3陶瓷硬质相的形成机制．利用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱分析仪（EDS）等设备进行检测分析．结果表明,堆焊层中原位合成了“十字开花状”、“短杆状”、“颗粒状”的TiC陶瓷硬质相和不规则“六角杆状”的M7C3陶瓷硬质相;部分TiC和M7C3陶瓷硬质相紧密结合,提高了TiC陶瓷硬质相与基体组织的结合强度;M7C3可以附着在TiC颗粒上生长,TiC硬质相的形成提高了M7C3的形核率．     

Effects of Al and Al4C3 contents on combustion synthesis of Cr2AlC from Cr2O3-Al-Al4C3 powder compacts

Preparation of the ternary carbide Cr₂AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from the Cr₂O₃-Al-Al₄C₃ powder compact. Effects of the contents of Al and Al₄C₃ on the product composition and combustion behavior were studied by formulating the reactant mixture with a stoichiometric proportion of Cr₂O₃:Al:Al₄C₃ = 3:5x:y, where x and y varied from 1.0 to 1.5. When compared to those of the powder compact with Cr₂O₃:Al:Al₄C₃ = 3:5:1 (i.e., x = y = 1.0), the combustion temperature and reaction front velocity increased with content of Al, but decreased with that of Al₄C₃. Besides Cr₂AlC and Al₂O₃, the final products always contained a secondary phase Cr₇C₃ that was substantially reduced by adopting additional Al and Al₄C₃ in the reactant compacts. For the sample with Cr₂O₃:Al:Al₄C₃ = 3:7.5:1 (x = 1.5), solid state combustion reached a peak temperature of 1245 °C and yielded Cr₂AlC with a trivial amount of Cr₇C₃. Although Cr₇C₃ was lessened by introducing extra Al₄C₃, the increase of Al₄C₃ from y = 1.1 to 1.5 produced almost no further reduction of Cr₇C₃ in the final product. This is partly attributed to the low combustion temperature in the range of 1065-1095 °C for the samples with additional Al₄C₃, and in part, due to the role of Al₄C₃ which might react with Cr to form Cr₇C₃, Cr₂Al, and Cr₂AlC.     

原位合成TiC-M7C3陶瓷硬质相显微组织的分析

采用等离子弧堆焊技术原位合成TiC-M7C3陶瓷硬质相,探讨堆焊层中TiC-M7C3硬质相对堆焊层耐磨性的影响.利用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱分析仪（EDS）、洛氏硬度计及湿砂磨损试验机等设备进行检测分析.结果表明,堆焊层是由高碳马氏体基体和大量弥散分布在基体中的TiC,M7C3陶瓷硬质相构成的过共晶组织;堆焊层表面的洛氏硬度为66.4 HRC,磨损量为0.086 g.TiC可以作为M7C3陶瓷硬质相的形核核心,提高了M7C3陶瓷硬质相的形核率,促使其晶粒细化;在TiC和M7C3陶瓷硬质相的共同作用下,Fe-Cr-Ti-C系合金比相同Cr元素含量的Fe-Cr-C系合金堆焊层的硬度更高,抗磨损性能更好.     

Effect of Cr7C3 on the mechanical, thermal, and electrical properties of Cr2AlC

In this work, phase pure Cr₂AlC and impure Cr₂AlC with Cr₇C₃ have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10⁻⁵ K⁻¹ in the temperature range of 25-1200 °C. The thermal conductivity of the Cr₂AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr₂AlC decreases from 1.8 × 10⁶ Ω⁻¹ m⁻¹ to 5.6 × 10⁵ Ω⁻¹ m⁻¹. For the impure phase of Cr₇C₃, it has a strengthening and embrittlement effect on the bulk Cr₂AlC. And the Cr₂AlC with Cr₇C₃ would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.     

VC, Cr3C2 doped ultrafine WC-Co cemented carbides prepared by spark plasma sintering

The influence of the addition of 0.3, 0.5 and 0.7 wt.% VC on the density, microstructure and mechanical properties of WC-Cr₃C₂-11 wt.% Co with 0, 0.2, 0.4 and 0.6 wt.% Cr₃C₂ hard metals prepared by spark plasma sintering (SPS) at a temperature of 1200 °C (5 min, 40 MPa) was investigated. Microstructure analysis revealed that the WC grain size in the sintered hard metals was strongly influenced by the VC and Cr₃C₂ content. With the addition of inhibitors and the increased amount of Cr₃C₂, the density is reduced, and on the contrary, the addition of VC as an inhibitor contributes to promoting the densification. The combined addition of Cr₃C₂ and VC could strongly reduce the WC grain growth to about 350 nm. Observation suggests that the fracture of WC-Co cemented carbide is brittle and intergranular. The amount of added VC/Cr₃C₂ should be controlled in a certain range. Samples with an appropriate proportion of VC/Cr₃C₂ added exhibit higher hardness which can be up to 1938 HV₃₀. Toughness, too, can reach 16.34 MPa m^1/2.     

Microstructure and abrasive wear performance of chromium carbide reinforced Ni3Al matrix composite coating

A Ni-Al-Cr₃C₂ welding wire was produced by metal-powder-core technique. When the welding wires were welded on the surface of carbon steel, under the effect of the physical heat of arc, Ni reacted with Al to form Ni₃Al and carbide particles reinforced Ni₃Al matrix composite was formed. Cr₃C₂ was decomposed during welding and dispersed Cr₇C₃ with stripe shape formed, which strengthened the matrix significantly. The Cr₇C₃-Ni₃Al interface has broadened into a zone of interdiffusion and a new phase M₂₃C₆, which indicates that a good bond has been formed. The pin-abrasion wear test showed that the abrasion resistance of Cr₇C₃/Ni₃Al composite is six times higher than that of Stellite12 alloy at room temperature. The good wear resistance of Cr₇C₃/Ni₃Al composite coating can be attributed to large volume fraction of carbides, high hardness, and good phases interface bond.     

横纵磁场下铁基合金堆焊层组织性能的对比分析

将Fe5自熔合金采用等离子弧堆焊设备堆焊到低碳钢表面,在堆焊的过程中施加直流横向和直流纵向磁场,并调节磁场参数和堆焊工艺参数,对不同参数下堆焊试样进行硬度和磨损试验,采用显微电镜和扫描电镜对堆焊层显微组织进行分析,研究两种磁场状态下堆焊层组织、性能的差异性,并对其中的机理进行探究.结果表明,直流横向磁场和直流纵向磁场均可提高硬质相的形核率,改善堆焊层的组织性能;横向磁场作用下堆焊层中硬质相杂乱分析,而纵向磁场使堆焊层中的硬质相以规则的"六边形"出现,这使得横向磁场对提高堆焊层的硬度较明显,纵向磁场对提高堆焊层耐磨性效果明显.