热绝缘剂在碳化钨电弧堆焊中的作用机理

分析了TIG碳化钨复合合金堆焊过程中,碳化钨颗粒的蚀损机理,台架实验结果表明,热绝缘剂对碳化钨硬质相的热防护作用主要发生在堆焊过程的焊条熔化阶段;一是消融隔热作用, 即包裹于碳化钨颗粒周围的热绝缘剂的分解吸热作用,降低了碳化钨颗粒在电弧高温环境中的本体温度;二是热绝缘剂分解后的残余碳延缓了碳化钨硬质相在铁基溶体中的熔损速度。     

碳化钨堆焊热保护技术

总结了碳化钨复合耐磨堆焊在工业各部门的应用及碳化钨在堆焊高温条件下发生的物理化学变化。针对近年来碳化钨堆焊中的热保护技术问题,从碳化钨绝热剂的选择、制备、防热效果评定等方面提出阿供实施的技术思路,并就与之有关的现代科学技术研究成果以及新理论新方法进行了简要陈述。     

一种用于碳化钨堆焊的管装电焊条的研究

提供一种用于碳化钨堆焊的管装电焊条。扫描电镜观察、能谱分析及显微硬度测试结果表明堆焊层中存在两种类型的硬质相 ,即 WC- W2 C共晶的原始碳化钨颗粒(硬度 HV2 0 12～ 2 34 1)和 M6C构成的 η相 (HV1817～ 2 2 14)。M6C相以粒状和团块状存在 ,与实芯焊条堆焊的金属中析出的鱼骨状共晶 M6C相比较 ,在不降低堆焊层硬度条件下 ,可提高堆焊层的强度和韧性指标。新型焊条中使用 D型热绝缘剂 ,减少了原始碳化钨颗粒的熔损 ,使焊缝金属组织中硬质相分布域直径 Dd 和面积分数 AC 分别提高2 5 %和 6 2 %。     

碳化铌对铁基碳化钨耐磨堆焊合金中碳化钨溶解的影响

采用自行研制的铁基碳化钨耐磨堆焊药芯焊丝,通过钨极氩弧焊(TIG)在Q235上制备Fe-Nb-C-B-Ni-WC(30%)合金.改变合金中铌含量(1.0%,2.5%,3.8%),研究铌含量对Fe-Nb-C-B-Ni-WC(30%)合金中碳化钨溶解的影响.结果表明,铌含量对合金中碳化钨的溶解程度有很大影响,优先在碳化钨周围生成的细小NbC对碳化钨溶解起抑制作用,而其生成量决定了抑制碳化钨溶解作用的强弱.铌含量为2.5%的合金中生成的NbC有效的抑制了碳化钨的溶解,使碳化钨颗粒保留的比较完整.     

碳化钨/高锰钢堆焊层的制备工艺及耐磨性能

采用氧乙炔焰在Q235钢基体上制备碳化钨/高锰钢堆焊层,通过调节碳化钨的种类、粒度和含量来对比组织、性能上的差异。试验结果表明,在堆焊层中碳化钨颗粒分布均匀,颗粒周围产生共晶组织,且堆焊层的硬度随着碳化钨颗粒的数量、碳化钨颗粒尺寸的增加而上升;耐磨性随着碳化钨颗粒度的减小和碳化钨数量的增加而增加,其含量达到40%时为最佳,经冲击强化后堆焊层性能进一步提升。     

金刚石焊接用热绝缘剂应用研究

本文借鉴热保护理论，选用有机聚合物FB树脂和无机的金属氢化物MH2作金刚石焊接热绝缘剂。测定了烧蚀金刚石试样的单颗粒抗压强度变化情况，对氧一乙炔焰堆焊试样进行了耐磨性试验，对试样做了SEM观察。所有实验表明：所选热绝缘剂有效地避免了金刚石在高温焊接时出现变质或石墨化，保持了金刚石的优异性能，使其高耐磨性得到充分发挥。     

碳化钨耐磨药芯焊丝电弧堆焊工艺与性能的研究

试验研究了碳化钨耐磨药芯焊丝电弧堆焊工艺方法对堆焊层性能和组织的影响。结果表明，堆焊工艺中的能量输入、堆焊层数以及冷却方式对堆焊层的硬度、耐磨性及堆焊层结合性能有明显的影响。导致堆焊层性能变化的主要原因是工艺因素引起了堆焊层组织及碳化钨形态的变化。其中堆焊工艺采用大电流、双道焊、缓慢的冷却速度时，堆焊层中的强化相碳化物颗粒较大，分布均匀，堆焊层具有良好的综合性能。     

利用等离子弧堆焊获得铁基合金+碳化钨硬质合金的复合堆焊层

利用新研制的外送碳化钨等离子弧焊枪系统 ,对F32 1铁基合金粉末和机械破碎的碳化钨硬质合金颗粒进行了堆焊 ,获得的复合堆焊层碳化钨合金颗粒分布均匀 ,堆焊层缺陷率低 ,焊道成型良好 ,碳化钨合金颗粒的质量分数可达 40 %～ 42 % ,堆焊后的碳化钨合金颗粒硬度值仍保持了原有的高硬度 ,颗粒表层重熔量小 ,合金元素扩散率低 ,获得的堆焊层胎体组织为马氏体 残余奥氏体 共晶 (马氏体 碳化物 ) ;碳化钨合金颗粒周围鱼骨状共晶没有扩散到胎体马氏体中 ,避免了复合堆焊层的整体脆化。试验对堆焊层的平均孔隙缺陷率进行了测算 ,测算结果为碳化钨合金颗粒平均孔隙缺陷率低于 1.5 % ,并对裂纹、孔隙分布及产生原因进行了分析     

碳化钨颗粒增强高锰钢基堆焊材料组织及耐磨性能的研究

为提高高锰钢堆焊层在低冲击或静载磨损条件下的耐磨能力,采用堆焊方法制备了碳化钨颗粒增强高锰钢基耐磨材料,并对焊层的微观组织及耐磨性能进行了分析。结果表明,适当的碳化钨颗粒加入量可获得碳化钨-高锰钢堆焊层,焊层中碳化钨颗粒分布均匀,界面结合良好,堆焊材料与单纯高锰钢焊层相比,抗静载磨损能力大幅度提高。     

钒对铁基碳化钨耐磨堆焊层组织和性能的影响

在自研制的碳化钨管状药芯焊条中添加不同含量的钒元素（0%~3%）并制备堆焊合金,通过SEM,XRD,EDS等研究分析手段,研究不同钒含量对碳化钨耐磨层组织性能的影响规律.结果表明,钒含量与堆焊层中碳化钨颗粒的溶解程度密切相关,钒优先将碳化钨颗粒分解出的碳原子以碳化钒形式固定,从而抑制了碳化钨颗粒的分解,钒元素含量决定了碳化钨溶解的强弱,含有2%钒元素的堆焊层中生成适量碳化钒有效抑制了碳化钨的溶解.钒元素的加入还能强化碳化钨堆焊层基体金属的硬度,降低堆焊层中碳化钨颗粒剥落的风险,有效提高了堆焊层的耐磨性.     

碳化钨条填充法电弧堆焊工艺及堆焊层泥沙磨损研究

介绍 了铸造碳化钨条填充法电弧堆焊制备金属基碳化钨陶瓷复合材料耐磨层的基本过程，叙述了该方法堆焊工艺特点及电弧烧作用对碳化钨颗粒形状及性能的影响，结合堆焊工艺论述了复合材料堆焊层的成分和性能特点。对铸造碳化钨条填充法电弧堆焊制备的复合材料堆焊层进行了泥沙磨损试验，并将其耐磨性与焊条熔敷金属的耐磨性进行了对比。讨论分析了作为硬质相的碳化钨颗粒的基体对堆焊层抗泥沙磨损性能的影响。     

Laser surfacing of nickel-based composite war-resisting coatings reinforced with tungsten carbide

Investigations were carried out into the phase and structural state of the gradient coating produced by laser surfacing using tungsten carbide powders in a cobalt coating and a nickel alloy. The results show that the structure contains the WC carbide with the particles of the carbide forming spherical agglomerates, a nickel solid solution, alloyed with iron and cobalt, Me₂W₆ intermetallic phase, where Me = Fe, Cr and also CrO₂ oxide. It is shown that the layers after reheating are characterized by the more extensive dissolution of the carbide and agglomerates and the formation of chromium-containing inclusions. The distribution of the elements and microhardness values in the cross section of the deposited coating was determined.     

碳化钨条氧乙炔焰堆焊层泥沙磨损试验研究

提高过流易损件的耐磨性及使用寿命是疏浚行业亟待解决的问题。作者运用氧乙炔焰堆焊法，制备出碳化钨条火焰堆焊层，介绍了这种堆焊的基本特点及工艺过程，对堆焊层的抗泥沙磨损性能及堆焊层中碳化钨颗粒分布和显微形貌等进行了分析讨论，研究表明：复合耐磨堆焊层中碳化钨颗粒的较少溶解、颗粒与胎体金属之间的良好结合以及“阴影效应”和“支撑作用”的共同作用是获得优异抗泥沙磨损性能的根本原因。     

Evaluation of wear mechanisms of Y-TZP and tungsten carbide punches

Tool wear is one of the major concerns in the tooling industry. A comparative evaluation of different tool materials and tool wear will help preventing frequent replacement of tools thus reducing the costs incurred due to such replacements. In this paper, tool wear mechanism of tetragonal zirconia polycrystal (TZP) punch is compared with that of commercially available WC (tungsten carbide) punch during stamping. The tool life for the TZP punch was found to be over 2.5 times higher than that of commercial tungsten carbide. The worn-out tools were analysed using scanning electron microscope and optical microscope for studying the tool wear mechanisms. Tool wear and chemical action possibly cause the failure of the tungsten carbide punch, whereas wear of TZP punch is predominantly caused by mechanical shearing of asperity and plastic deformation. Due to their inherent high melting point and the absence of the second-phase binder, ceramics materials do not soften at higher temperature unlike the carbide tools. Hence, they can be used at high cutting speeds without initiating deformation/diffusion wear. This assists in improving the tool life significantly. In addition, TZP ceramics is inert, corrosion resistant and non-wetting when contacting metals. Exposed carbide grains act as a site for increased wear and metal pickup during precision, high-speed metal stamping and forming. Moreover, cobalt-depleted carbide tools can create burring of the strip being stamped, leading to poor part quality. The performance of TZP punch tool will be evaluated thoroughly based on experimental data in this paper.     

The effect of consolidation parameters on the mechanical properties of binderless tungsten carbide

This paper discusses the effect of the process parameters on the mechanical properties of binderless pure tungsten carbide during a GPS (gas protection sintering) process. The result of experiments reveal that the mechanical properties of the material increases with raising the sintering temperature and extending the retention time; however a decreased hardness was observed as a result of abnormal grain growth under higher sintering temperatures. The results of XRD and EDS analyses confirmed the absence of brittle phases such as W₂C or impurity phases in the microstructure. The optimized process parameters for GPS process are identified as: a mean particle size of 1.03 μm, a sintering temperature of 1860 °C and a retention time of 60 min; the resulting mechanical properties are: a relative density of 95.1%, a micro-hardness of 1718 kgf/mm² and a fracture toughness of 5.97 MPa m^1/2. The width of particles size distribution has a significant effect on the density and hardness of the sintered material however the width of particles size distribution is dependent on the original particle size. Finally, ultra-fine particles increase the chance of conglomeration and sub-micron structures. The conglomeration of ultra-fine particles hinders the filling of porosities during sintering and lowers the density and hardness of the material.     

Synthesis of high-purity ultrafine tungsten and tungsten carbide powders

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO_2.9 and the following deep reduction with H₂ or carbonization with CH₄+H₂ mixed gases. The effects of C/WO_2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO_2.9 ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO₂. With changing C/WO_2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO_2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively.     

Oxidation of tungsten and tungsten carbide in dry and humid atmospheres

Oxidation experiments were performed on pure tungsten and hot-pressed tungsten carbide. The chemical state and thickness of the oxide products were determined by ESCA. The oxidation of W and WC in dry atmosphere was performed in oxygen at temperatures ranging from 20 to 500 °C. The oxide formed is WO₃. The thickness of the oxide layer increases slowly up to 200 °C, after which the oxide growth is rapid.

The oxidation behaviour of W and WC in humid atmospheres was studied at room temperature in air at relative humidities of 60 and 95%. It was found that the thickness of the oxide layer increases with increased humidity. No formation of hydroxide was observed. Exposing W to water for one week results in a thick layer of WO₂, WO₃ and hydroxide. In the case of WC no oxide at all was visible after exposure to water. Furthermore, WC is resistant to further oxidation after exposure.