Tool steel and copper coatings by friction surfacing - A thermography study

Infrared thermography was used to record thermal profiles during friction surfacing. Thermal profiles for different sets of consumable rod/substrates (tool steel/steel; copper/steel and copper/copper) were recorded and analyzed. The thermal profiles showed distinct stages of plastic deformation with respect to temperature. The mechanism of bonding or no-bonding was discussed based on thermal profile data. It was found that a metallurgically bonded coating can be obtained if the flow stress of the plasticized material is comparable with the localized stress developed due to axial loading.     

Wear behaviour of thermal flame sprayed FeCr coatings on plain carbon steel substrate

The principle aim of this study is to investigate the wear behaviour of FeCr coatings on Ni-based bond deposited plain carbon steel substrate for several applications in power generation plants. For this purpose, FeCr and Ni-based powders were sprayed on plain carbon steel substrates using a thermal flame spray technique. Fabricated layers were characterized by using a X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), microhardness and surface roughness testers. FeCr coatings were subjected to sliding wear against AISI 303 stainless steel counter bodies under dry and acidic environments. A pin-on-plate type of apparatus was used with normal loads of 49 and 101 N and sliding speed of 1 Hz. XRD results revealed that FeCr, Fe, Cr, Fe–Cr–Ni, γ-Fe₂O₃ and Fe₃O₄ phases are exist in the coating. In addition, some inhomogenities such as oxides, porosity, cracks, unmelted particles and inclusions were observed by SEM. The surface morphologies of FeCr samples after wear experiments were examined by SEM and EDS. It was found that friction coefficients of the coatings in dry condition are higher than that in acidic environment.     

Transferring mechanism of the coating rod in friction surfacing

A coating rod of 1Cr18Ni9Ti (321) was deposited on the substrate of mild steel 1020 to be able to perform a friction surfacing experiment. The temperature changes of special points on the coating rod were measured using a thermocouple. The results show that the temperature increase rate at the friction interface reached a high level at first. Then the rate decreased to a low level once the friction system became quasi-steady and the temperature became approximately stable near the melting point of the coating rod. The theory of contact melting was used to build the physical model for the quasi-liquid layer. Subsequently, the corresponding calculations were carried out. The computer simulation results are found to be consistent with the experiment results, and as such, the present study demonstrates the feasibility of applying contact melting theory to the study of friction surfacing. Likewise, this study reveals that the material at the top of the coating rod is plastic, and that it behaves as a quasi-liquid in the friction surfacing process. The study establishes the theory basis for the study of the mechanism of friction surfacing, and provides a new method for investigating other friction-welding techniques.     

The microstructure of composite cermet coatings produced by carbo-vibroarc surfacing

The results of investigation of the microstructure of composite coatings produced by carbo-vibroarc surfacing using cermet pastes are presented. It is shown that the composite cermet coating consists of two zones – the main and transition. The main zone of the coating contains the Fe₂B hardening phase with nickel and chromium atoms implanted in the crystal lattice of the phase. The zone is situated in the matrix of the solid solution of iron and nickel Ni₃Fe. The transition zone of the coating is formed by the mutual diffusion of the coating and the substrate and consists of the (Fe, Ni)₂B hardening phase and the Ni₃Fe matrix. It is also shown that the hardening phases form plate-shaped grains with thicknesses of 1–4 μm and more than 100 μm long, distributed in the form of colonies throughout the entire volume of the coating zone. In the direction to the transition zone, the shape of the structural components changes to circular with the diameter of up to 5 μm.     

Development of in-situ composite surface on mild steel by laser surface alloying with silicon and its remelting

In the present study, an attempt has been made to develop in-situ iron silicide dispersed surface on mild steel substrate by laser surface alloying with silicon using a high-power continuous wave CO₂ laser. The effect of laser surface remelting of the alloyed surface using argon and nitrogen (with and without graphite coating) as shrouding environment has also been studied. The microstructure of laser surface alloyed mild steel with silicon consists of uniformly dispersed iron silicide in grain refined α-iron matrix with an improved microhardness to 575 VHN as compared to 150 VHN of as-received mild steel substrate. Surface remelting in Ar atmosphere coarsened the microstructure and reduced the area fraction of silicide and hence, reduction in the microhardness to 450 VHN. Surface remelting in nitrogen increased the microhardness to 740 VHN due to the formation of iron nitrides in addition to the presence of silicides. Graphite coating prior to remelting improved the microhardness to 800 VHN due to the presence of martensites along with nitrides and silicides. A maximum enhancement in wear resistance was achieved when remelting was done in nitrogen environment with carbon deposition. The mechanism of wear was found to be predominantly abrasive in nature as compared to adhesive and oxidative in as-received mild steel.     

Q235钢表面CMT堆焊310不锈钢的组织与性能

采用自动CMT (Cold metal transfer) 焊工艺,在Q235钢板堆焊了H12Cr26Ni21Si不锈钢,焊接电流为108 A,焊接电压为15.8 V,摆动宽度为12 mm,摆动速度为23 mm/s,焊接速度为2 mm/s,堆焊搭接量为7 mm,获得了成型美观、致密无缺陷的不锈钢堆焊层。对堆焊层的显微组织、化学成分进行了分析,测试了堆焊层的显微硬度及与基体结合强度。结果表明,堆焊层组织为奥氏体树枝晶和等轴晶;Ni,Cr,Fe是组成堆焊层的主要元素;堆焊层硬度高于基体;堆焊层与基体的结合界面的抗剪切强度大于405 MPa。     

Neurofuzzy approach to process parameter selection for friction surfacing applications

Friction surfacing is an advanced manufacturing process, which has been successfully developed and commercialised over the past decade. The process is used for corrosion and wear resistant coatings and for reclamation of worn engineering components. At present, the selection of process parameters for new coating materials or substrate geometries experimentally requires lengthy development work. The major requirement is for the flexibility to enable rapid changes of process parameters in order to develop new applications, with variations of materials and geometries in a cost effective and reliable manner. Further improvement requires development of appropriate mathematical models of the process, which will facilitate the introduction of optimisation techniques for efficient experimental work as well as the introduction of real time feedback adaptive control. This paper considers the use of combined artificial intelligence and modelling techniques. It includes a new frame of a Neurofuzzy-model based Decision Support System — FricExpert, which is aimed at speeding up the parameter selection process and to assist in obtaining values for cost effective development. Derived models can then be readily used for optimisation techniques, discussed in our earlier work.     

Microstructures and ion-irradiation behaviour of friction stir welded 12Cr-ODS steel

12Cr oxide dispersion strengthened steel was successfully joined by friction stir welding (FSW), and the joints were irradiated with 3?MeV Au ions at 500°C. The morphology of grains, dislocations, sizes and distributions of nano-sized oxide particles (NPs) in different zones of the FSW joints were analysed. It was found severe plastic deformation occurred and fine equixed grains were formed in stir zone (SZ). The NPs coarsen obviously in thermal-mechanically affected zone (TMAZ) on advancing side (AS) due to the relative movements of plastic materials with high-velocity gradient. The size distributions of the NPs in base metal (BM), heat affected zone (HAZ) and RS-TMAZ are concentrated in a smaller range than those in SZ and AS-TMAZ. Finer grains and high density of dislocations result in hardness increasing obviously in SZ. Irradiation introduced higher hardening in HAZ because of its less grain boundaries and dislocation density compared with SZ and BM.     

Friction surfaced tool steel (H13) coatings on low carbon steel: A study on the effects of process parameters on coating characteristics and integrity

Tool steel H13 was friction surfaced on low carbon steel substrates. Mechtrode (consumable rod) rotational speed and substrate traverse speed were varied, keeping the axial force constant. The effects of process parameters on coating characteristics and integrity were evaluated. A process parameter window was developed for satisfactory deposition of tool steel coatings. Coating microstructures were examined using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Microhardness tests, shear tests, and bend tests were conducted on coatings. The results show that coating width is a strong function of mechtrode rotational speed, while coating thickness is mainly dependent on substrate traverse speed. Lower mechtrode rotational speeds results in wider coatings, while higher substrate traverse speeds produce thinner coatings. Thinner coatings exhibit higher bond strength than thicker coatings. Coatings show no carbide particles, yet exhibit excellent hardness (above 600 HV) in as-deposited condition due to their martensitic microstructure.     

铝/钢多层多道耗材摩擦焊接头组织性能研究

采用耗材摩擦焊实现2A12铝合金在Q235低碳钢上的多层多道焊接。结果表明:耗材摩擦焊可以获得表面成形良好、无内部缺陷的多层多道焊接接头。在焊接热循环作用下,堆焊层组织中第二相颗粒发生了聚集长大且先堆焊层第二相颗粒聚集长大现象更明显;接头后堆焊层硬度高于先堆焊层硬度;接头剪切强度可达130.3 MPa,为2A12铝合金剪切强度的63%,接头断裂于堆焊层铝合金侧,断裂方式为韧性断裂。     

2209和2507双相不锈钢堆焊层组织结构及耐蚀性对比

利用光学显微镜、X射线衍射仪、扫描电子显微镜和能谱仪等,对2209和2507双相不锈钢FCAW堆焊层焊态、退火态的组织结构和耐蚀性进行对比研究。结果表明：两种堆焊层焊态时均主要由铁素体α和魏氏体状奥氏体γ组成,在α晶内及α/γ界面处存在少量细条状的二次奥氏体γ2,在α/γ、α/α界面处还存在极少量的点状σ相;两种堆焊层经690℃×8h退火后,σ相和γ2均明显增多。两种堆焊层焊态的耐蚀性均合格,且2507型堆焊层的耐蚀性优于2209型堆焊层;而两种堆焊层退火态的耐蚀性均急剧下降、严重不合格,这主要是由于退火过程中堆焊层内析出大量σ相和γ2所致。     

刮板机高强耐磨钢堆焊工艺

针对煤炭输送设备刮板输送机顺槽中板的磨损失效问题,开展了高强耐磨钢的堆焊工艺研究。采用高碳高铬药芯焊丝在高强耐磨钢上进行堆焊试验,试验发现高强耐磨钢堆焊存在严重的软化现象。采用及时冷却措施,在高强耐磨钢上进行了冷堆焊工艺试验,实验表明冷堆焊有效降低了软化区域,提高了耐磨性,解决了高强耐磨钢堆焊难点,增强了高强耐磨钢在刮板输送机中的应用效果,提高了刮板机极易磨损部位的耐磨性。     

Impact of tool wear on joint strength in friction stir spot welding of DP 980 steel

Abstract

Friction stir spot welding has been shown to be a viable method of joining ultra high strength steel, both in terms of joint strength and process cycle time. However, the cost of tooling must be reasonable in order for this method to be adopted as an industrial process. Recently a new tool alloy has been developed, using a blend of polycrystalline cubic boron nitride (PCBN) and tungsten rhenium (W–Re) in order to improve the toughness of the tool. Wear testing results are presented for two of these alloys: one with a composition of 60% PCBN and 40% W–Re, and one with 70% PCBN and 30% W–Re. The sheet material used for all wear testing was 1·4 mm DP 980. Lap shear testing was used to show the relationship between tool wear and joint strength. The Q70 tool provided the best combination of wear resistance and joint strength.     

Thermomechanical deformation behaviour of DH36 steel during friction stir welding by experimental validation and modelling

Friction stir welding is a solid state thermomechanical deformation process from which the plasticisation behaviour of the stirred material can be evaluated through the study of flow stress evolution. Flow stress data also supporting the development of a local microstructural numerical model have been generated. Hot compression testing of DH36 steel has been performed at a temperature range of 700–1100°C and strain rates from 10^?3 to 10² s^?1 to study the alloy’s thermomechanical deformation behaviour in conditions that simulate the actual friction stir welding process. It has been found that the evolution of flow stress is significantly affected by the test temperature and deformation rate. The material’s constitutive equation and constants have been calculated after analysis of these data. Preliminary numerical analysis results are in good agreement with experimental observations.     

Coefficient of friction and wear of sputtered a-C thin coatings containing Mo

The paper reports on preparation of ~ 3000 nm thick a-C coatings containing Mo, interrelationships between their mechanical properties, a coefficient of friction μ and wear rate k and the effect of Mo content in the a-C coating on these interrelationships. The Mo-C coatings were prepared by sputtering using an unbalanced magnetron (UM) equipped with a graphite targets (∅ = 100 mm, 99.9% purity) fixed to the UM cathode with Mo ring of different inner diameter ∅_i. The content of Mo in the a-C coating was controlled by ∅_i. It is shown that μ and k of the coating strongly depend not only on its hardness H but also on its effective Young's modulus E^? = E/ (1 − ν²), the ratios H/E^?, H³/E^?2 and the elastic recovery W_e; here E is the Young's modulus and ν is the Poisson ratio. The ratio H³/E^?2 characterizes the resistance of coating to plastic deformation. Coatings with a low amount of Mo composed of nanograins of carbides dispersed in a-C matrix exhibit low values of μ ≈ 0.07 and k ≈ 10^− 7 mm³/Nm measured with WC ball at the rotation speed v = 0.05 m/s, total sliding length l = 1000 m and the load L = 2 N.     

Corrosion behaviour at the interface of steel bars embedded in cement slurries: Effect of phenol polymer coatings

Cyclic voltammetry has been employed to investigate the behaviour of carbon steel and stainless steel electrodes in solutions obtained by filtering of calcium aluminate cement and portland cement slurries. Electro-polymerized phenol coating on steel electrodes has also been studied in carbonate medium. The phenol electro-polymerization occurs on a passivated surface and leads to adherent and stable polymeric film exhibiting a partial protection against corrosion. The Fourier transform infrared–attenuated total reflection spectroscopy shows that this film maintains the aromatic character and contains ether-linked rings.     

铜钢异种材料摩擦堆焊工艺优化

摩擦焊是最近几年发展较快的新型摩擦焊接技术之一。国内外学者对铁合金之间的焊接方法研究较为深入,但对铁铜异种材料之间焊接的研究尚不多见。通过大量实验,研究旋转速度为800~1 200 r/min、焊接速度为20~50 mm/min时焊接接头抗拉强度的变化。结果表明,当旋转速度为1 000 r/min、焊接速度为30 min/mm时,铜钢异种材料摩擦堆焊的接头平均抗拉强度是母材强度的89%,并且焊接质量最好。     

Tribological behavior of CrN/WN multilayer coatings grown by ion-beam assisted deposition

CrN monolayer coating and CrN/WN multilayer coatings were deposited on the silicon (100) substrate by ion-beam assisted deposition process. The bilayer period of these coatings was controlled at 8 nm and 30 nm. The cross-sectional morphology of nanoscaled multilayer coatings was characterized by scanning electron microscopy and transmission electron microscopy. The wear resistance of CrN/WN multilayer coatings and CrN monolayer coating was investigated using a pin-on-disc tribometer. The surface roughness (Ra) of the coatings was evaluated by atomic force microscopy, and that of CrN and WN monolayer coating was 6.7 and 5.9 nm, respectively. The employment of multilayer configuration in CrN/WN coating with bilayer period of 8 nm and 30 nm effectively reduced the surface roughness down to 1.9 and 2.2 nm, respectively. The friction coefficient of CrN monolayer coating and CrN/WN multilayer film with a bilayer period of 30 nm was 0.63 and 0.31, respectively. Owing to the high hardness/elastic modulus ratio, as well as the dense structure and the smooth surface roughness, the CrN/WN multilayer coatings exhibited better wear resistance in the consideration of friction coefficient and the worn surface morphology.     

Pulsed electrode surfacing of steel with TiC coating: Microstructure and wear properties

In the present study, pulse electrode surfacing (PES) technique was employed to deposit ultrahard and wear-resistant titanium carbide (TiC) coating on AISI 1018 steel. Wear resistance of the coated surface increased significantly. An attempt was made to correlate the thermodynamic predictions and experimental observations. A composite coating that is adherent, crack free, and defect free in nature was obtained, with TiC being the most stable phase. Islands of TiC of various shapes and sizes are present in the Fe-rich matrix in the coating. Microhardness measurements suggest high hardness values in the coating region. Tribological properties such as wear resistance and coefficient of friction were also measured. The coefficient of friction data do not show significant fluctuations. Wear and friction phenomena in such a coating have been explained on the basis of a model based on composite/multiphase material.     

转向架用Q345C钢堆焊接头组织及盐雾腐蚀行为

通过金相组织分析、力学性能试验、极化曲线试验和盐雾腐蚀试验,对比研究Q345C母材及其堆焊接头组织、力学性能及耐蚀性能。结果表明,堆焊接头组织与母材相比具有一定的差异。母材的冲击韧性优于堆焊焊缝。在相同试验条件下,Q345C母材及其堆焊接头腐蚀初期表面均出现橘红色的锈层,随着试验的进行,锈层逐渐加深,绝大部分橘红色锈层变为黑褐色锈层腐蚀产物。堆焊焊缝的腐蚀倾向、腐蚀速度和腐蚀失重均低于母材,但相差不大,其耐蚀性能稍优于母材。