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41.
The principal aim of this study was to compare the sliding wear performance of as-sprayed and Hot Isostatically Pressed (HIPed)
thermal spray cermet (WC-12Co) coatings. Results indicate that HIPing technique can be successfully applied to post-treat
thermal spray cermet coatings for improved sliding wear performance, not only in terms of coating wear, but also in terms
of the total volume loss for test couples. WC-12Co coatings sprayed by a HVOF system were deposited on SUJ-2 bearing steel
substrate and then encapsulated and HIPed at 850 °C for one hour. A high frequency reciprocating ball on plate rig was used
to measure the sliding wear resistance of these coatings in dry conditions under steel and ceramic contact configurations
at two different loads. Results are discussed in terms of coating microstructure, microhardness, fracture toughness and residual
stress evaluations. Microstructural investigations indicate fundamental changes in grain morphology, whereas x-ray diffraction
revealed beneficial transformations in phase composition of these coatings during the HIPing post treatment. The effects of
these microstructural changes on the physical properties and wear resistance are discussed. 相似文献
42.
This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools
in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out
on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism
of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes
are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting
force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during
these various cutting conditions. A summary of the results are as follows : (1) From the SEM direct observation in cutting
the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in
which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is
comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees
and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to
the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as
the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the
flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in
the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast
iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient
cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case,
it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut
was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance
was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was
due to the flank wear within the maximum value of Vmax being about 260 μ. 相似文献
43.
44.
Hot pressed silicon nitride that was exposed to high (90%) and low (32%) relative humidity was examined in ball-on-disc geometry against cemented carbide ball at various normal loads. The study indicated that Si3N4 tested at high R.H. gave less specific wear rate compared with Si3N4 at low R.H. The friction coefficient of Si3N4−WC-6% Co tribopairs was found in the range of 0.32–0.39 and 0.05–0.17 at low humidity and high humidity respectively. It is suggested that adsorbed moisture markedly affected the wear and friction properties of silicon nitride.Following the tests, SEM was used to elucidate the wear mechanism and particularly to delineate the effects of relative humidity on the wear and friction. SEM micrographs showed that the main wear mechanism at low relative humidity (32%) was caused by mechanical wear including abrasive grooves, large holes and polishing, whereas at high relative humidity (90%) the main mechanism was highly influenced by a tribochemical reaction related to the moisture adsorption from the environment. It is concluded that the removal of lubricious tribolayer was occurred by delamination induced crack propagation. 相似文献
45.
采用一种自制的WC-Co基合金作轧钢导卫辊材料,在轧制2000t45钢后用SEM和洛氏硬度计等对其表面形貌及硬度进行了分析和研究。结果表明:合金的主要磨损机制是体积塑性变形、犁沟效应和疲劳磨损。硬度由使用前的56HRC下降到49HRC,硬度下降的主要原因是合金表面部分晶粒在(受到冲击滑动摩擦作用)高速剪切变形条件下发生了动态再结晶,形成了200nm左右的细小晶粒。微细晶粒形成符合一种渐进式位相向差亚晶合并再结晶机制。 相似文献
46.
本文主要研究了热镀锌机组喷涂碳化钨的工艺辊在使用过程中发生表面喷涂层发生剥落的原因。 工艺辊基
体材质为 45 号钢, 表面采用超音速喷涂碳化钨涂层, 该工艺辊服役不到一年时间, 发现辊面中部喷涂层剥落。
针对辊面喷涂层剥落问题, 进行了喷涂材料的成分分析、 涂层的微观分析等。 研究发现喷涂前的喷砂工艺非常关
键, 在喷涂层剥落之处可以发现残留的砂粒。 通过涂层断面分析, 进一步的证明了在喷涂前的喷砂毛化工序中,
没有完全清除残留的砂粒会导致在使用过程中喷涂层的剥落。 相似文献
47.
Abrasion resistance of nanostructured and conventional cemented carbides 总被引:10,自引:0,他引:10
The abrasion resistance of nanostructured WC-Co composites, synthesized by a novel spray conversion method, is determined and compared with that of conventional materials. Scratching by diamond indenter and abrasion by hard (diamond), soft (zirconia) and intermediate (SiC) abrasives was investigated. The size of the scratch formed by the diamond is simply related to the hardness of the composite. Plastic deformation, fracture and fragmentation of the WC grains increase with their size. Nanoscale composites show purely ductile scratch formation. Nanocomposites possess an abrasion resistance approximately double that of the most resistant conventional material: this is a higher gain than the increase in hardness which is at most 23%. This large gain is due to a specific grain size effect on abrasion resistance in the case of diamond and SiC abrasive and to a very rapid increase of abrasion resistance with hardness in the case of the softer (SiC and ZrO2) abrasives. The observation of the abraded surfaces of conventional composites reproduced the known mechanisms: plastic deformation and fracture of WC grains by hard abrasives; removal of binder phase and fall-out of WC by soft abrasives. Magnetic fields from the ferromagnetic Co prevent the observation of abrasion mechanisms in the very fine-structured nanocomposites. 相似文献
48.
Three ceramic composite grades, consisting of a ZrO2 matrix and 40 vol.% WC, TiC0.5N0.5 or TiN phase, were completely self-developed by hot pressing powder mixtures of yttria-stabilised zirconia (Y-TZP) and distinctive WC, TiC0.5N0.5 or TiN powder sources. The friction and wear characteristics of the zirconia-based composites against WC-Co cemented carbide were investigated by performing dry reciprocating sliding experiments on a pin-on-plate tribometer under various normal contact forces. The generated wear was quantified using surface scanning topography. Post-mortem obtained wear volumes were correlated to real-time recorded wear depth. The ZrO2-40 vol.% WC grade displayed more favorable tribological properties compared to the other grades with equal secondary phase content. The worn surfaces and the wear debris were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), revealing several wear mechanisms such as polishing, abrasion and wear debris layer formation, mainly depending on the imposed contact load and the material composition. 相似文献
49.
Investigation of the residual stresses and microstructural properties associated with HVOF thermal spray coating of WC-17 wt% Co of same thickness on three substrates with coefficients of thermal expansion different to that of WC. The residual stresses were measured by X-ray diffraction sin2ψ techniques using CoKα radiation. The results indicated residual stresses that have different natures for the as-sprayed coatings despite using the same powder as feedstock. The magnitudes of the stresses in the as-sprayed condition are low. 相似文献
50.
采用低压烧结技术制备了不同Cr含量的WC-8Co硬质合金,通过XRD、SEM和力学性能测试等手段分析了Cr含量对硬质合金物相、显微结构和合金的力学性能的影响。结果表明,当Cr含量<0.9%时,合金由WC+γ-(WC)相组成,添加量增至0.9%及以上时,组织中出现缺碳相Co3W3C;随着Cr含量的增加,WC晶粒不断细化,当添加量为0.6%时,合金的综合力学性能最佳,其抗弯强度、维氏硬度及断裂韧性分别为3885MPa、1632.4HV30、9.82MPa.m1/2。 相似文献