民主德国的堆焊工艺及其现代化设备

本文介绍了民主德国关于堆焊工艺的一些最新研究成果以及为提高焊接自动化程度对设备的研究和发展。哈雷中央焊接研究所研制的堆焊-裁荷-填充材料-工艺系统(“A—B—Z—V”),作为选择工艺及填充材料的依据,从构件分析出发,生产了用于旋转件的特种程序的机器人ZIS12—63.孔堆焊设备ZIS12—96,轨道堆焊机ZIS13—43,轻便堆焊机ZIS15—40.以及用于侧板堆焊的机器人和煤球模型堆焊机器人。     

Sliding wear resistance of Fe-, Ni- and Co-based alloys for plasma deposition

Performance of Fe-, Ni- and Co-based alloys was evaluated in sliding wear and in the impact wear tests to simulate wear of valves and valve inserts in internal combustion engines. From the SEM investigations adhesive wear was confirmed by metal transfer between rubbing surfaces while surface deformation testify to abrasive wear. It was found that oxides formed on the surface prevented direct metal-to-metal contact and reduced the coefficient of friction thereby reducing wear. A comparison of wear resistances of Fe, Ni- and Co-based alloys used as hardfacings were given. It is also shown that Ni–Co alloys with Ni-alloy content between 40.4 and 64.3 have a considerable potential, they reveal above 2 times higher wear resistance than plasma-deposited cobalt alloy.     

Research About Microstructure and Wear Resistance of Hardfacing Layer on Cast Iron

It's simple technology to manufacture big trimming die by hardfacing on the base metal of cast iron. The chemical composition, microstructure, hardness, wear resistance and wear mechanism of the hardfacing layer were studied.The experimental results indicate that the hardfacing technology has much more advantages and cheaper than that of traditional process. The chemical composition, microstructure, hardness of the hardfacing metal are all satisfied for manufacturing the big trimming die by welding on cast iron. The wear resistant test of hardfacing layers were carried out by using two different electrodes. The wear resistance of new electrode hardfacing layer is higher than that of normal hardfacing electrode D322. The wear mechanism of hardfacing layer is belongs to abrasive wear model.     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Dual Coating Laser Cladding of NiCrBSi and Inconel 718

This paper presents an alternative approach to obtaining crack- and pore-free NiCrBSiFeCuMoC hard coatings on a low alloy steel substrate through coaxial laser cladding, by using Inconel 718 as a buffer layer between the hard coating and the base material. The presence of the buffer layer reduces the overall cracking susceptibility of the hardfacing material by reducing the compressive stresses developed during the cladding process and ensuring a more uniform heat distribution gradient at the surface of the material than the base metal alone, which provides an additional hardness and wear coefficient increase of 7% and improves the corrosion resistance of the obtained materials by 20%, in comparison with the reference sample obtained without an intermediate layer, by using the same operational parameters and minimizes elemental dilution with the substrate. Our method could prove useful in increasing the quality and life cycle of expensive high-performance hard-coated materials, especially those working under demanding operational and environmental conditions.     

Delamination failures of Stellite hardfacing in power plants: a microstructural characterisation study

In recent years, several incidents of cracking and failures have been observed in Stellite (Stellite is a registered trademark of the Deloro-Stellite Corporation) hardfacing used in valves of modern high temperature combined cycle gas fired power plants. These hardfacing layers are applied as an overlay onto a steel substrate, such as CrMo steel (i.e. Grade 22, WC9) or creep strength enhanced ferritic steel (i.e. Grade 91, C12A). Cracking has been observed in valve components at the Stellite/steel interface and in the weld dilution zone formed between the steel and clad. Ultimately, disbonding or delamination of the weld hardfacing from the valve body occurs and has resulted in collateral damage to components in the plant (such as to the turbine) or valve failure. In this study, the microstructure formed near the Stellite/steel interface is investigated. Based on thermodynamic modelling, microstructure formed at these regions is hypothesised and a simple methodology is proposed to predict the occurrence of these failures.     

Optimisation of cobalt-based hardfacing in carbon steel using the fuzzy analysis for the robust design

In this paper, we present the application of the fuzzy logic analysis to a Taguchi orthogonal experiment for developing a robust model with high efficiency in multiple performance characteristics (MPCs) of the plasma transfer arc welding (PTAW) hardfacing process. It eliminates uncertain information and is a simple, effective, and efficient approach. A fuzzy logic system is used to simultaneously investigate relationships between various MPCs and to determine the efficiency of each trial of the Taguchi experiments. From the fuzzy inference process, we are able to determine the optimal setting of factor-levels for the MPCs. In addition, we also use the analysis of variance (ANOVA) to identify the significant factors, which coincide with findings from the fuzzy logic analysis and are found to account for about 79% of the total variance. Furthermore, a confirmation experiment of the optimal process is conducted, and it verifies that both individual performance characteristics and MPCs are successfully optimized and satisfy our desired levels of MPCs.     

NiCrSiBC alloy: microstructure and hardness of coatings processed by arc and laser

The processing technique is decisive for the characteristics of a coating. This is because the heat supply, which depends on the technique and on the parameters, has an influence on the dilution and the solidification rate. In alloys with low metallurgical complexity, the effect of processing with deposition techniques that give a higher cooling rate may be translated into refining of the microstructure. A more refined microstructure is expected to result in higher mechanical strength of the coating. However, in the deposition of alloys that are more complex metallurgically this does not always occur, because the high cooling rate may suppress formation/precipitation of phases responsible for strength. The influence of processing on the microstructure and hardness of coatings of alloy Colmonoy-6^® was assessed in this study. The alloy was processed by plasma transferred arc and high-power diode laser on plates of AISI 304 with two levels of dilution. In both cases, good-quality, defect-free coatings were obtained. Increase in Fe content (dilution) and different cooling rates result from processing with different parameters and techniques. This leads to significant changes in microstructure and hardness of the coatings, associated with the distribution, morphology and chemical composition of the carbides and particularly of the borides.     

Effect of carbide degradation in a Ni-based hardfacing under abrasive and combined impact/abrasive conditions

Within this work, the effect of carbide degradation in a WC/W₂C reinforced Ni-based hardfacing was assessed under abrasive and combined impact/abrasive conditions. In view of the above, a WC/W₂C reinforced Ni-based hardfacing was deposited by plasma transferred arc (PTA) welding using different welding currents. Microstructure was characterised by quantitative metallography to determine specific structural parameters: mean carbide diameter and carbide area fraction. Scanning electron microscopy (SEM, EDS) and X-ray diffraction (XRD) were also used to characterise carbide dissolution mechanism. Tribological behaviour was determined with a 3-body abrasion test according to ASTM G65 and with a cyclic impact/abrasion test (CIAT). Results showed significant carbide degradation with increasing welding current, resulting in a significant reduced primary carbide content and carbide diameter. Reduced carbide content indicated a significantly wear rate increase under pure 3-body abrasion conditions. Specific wear energy was determined under pure abrasive condition and showed significant dependence on the primary carbide content. However, wear rates under combined impact/abrasion were at constant level due to the reduction of the brittle primary carbide content.     

Coatings enrichment by carbide dissolution

Surface welding of hard alloys allows for the protection of components exposed to severe wear. Nevertheless, deposition of these hard alloys requires special procedures in order to minimize cracks and other welding defects. This work evaluated an alternative procedure to reduce welding defects as hard surfaces were produced. For that purpose fine WC-Co were mixed with iron powders and with an atomized cobalt based alloy, respectively, and processed with Plasma Transferred Arc (PTA). Powder mixtures with 5 wt.% and 35 wt.% WC-Co were deposited with two current intensities 150 A and 170 A on carbon steel plates. It was aimed to melt and dissolve the carbides to produce defect free hard iron based and cobalt based coatings. Surfaces were characterized for their soundness, hardness and microstructure regarding the effect of powder mixture chemical composition and current intensity used during processing. Visual inspection, dilution measurements, X-ray diffraction of powder mixtures and coatings, Vickers microhardness, optical and Scanning Electron Microscopy and pin-on-disc tests were used for surface evaluation. Results showed that PTA deposition allowed for the enrichment of coatings as carbides were melted in the plasma arc and dissolve in the different matrix.