CATHODIC PROCESS AND WEAR RESISTANCE OF ELECTRO-DEPOSITED RE-Ni-W-P-SiC COMPOSITE COATING

Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.

Influence of processing parameters on microstructure and wear resistance of Ti+TiC laser clad layer on titanium alloy

Laser cladding experiments were carried out on Ti-6Al-4V alloy with Ti+33%TiC(volume fraction) powders. Laser processing parameters were studied systematically to investigate the influences on the surface quality. Microstructure, microhardness and wear resistance of the clad layer were evaluated. The results show that the laser parameter has considerable influence on microstructure and wear resistance of laser clad layer. With the optimized technical parameters, a clad layer with good surface quality and uniform microstnicture was obtained. The microhardness of the clad layer HV0.2 is 1 080, and the wear rate is reduced by 57 times.

Influences of Tool Wear on Residual Stress and Fatigue Life of Workpiece in Hard Cutting Process

Tool wear has an important influence on the residual stress distribution on the machined surface.Also,it will influence the fatigue life of finished workpiece. In this research,the hard turning process of hardened die steel Cr12 MoV was studied by using PCBN tool with considering tool wear. Based on the numerical treatment of residual stress,the dispersion and distribution curves of different tool wear were fitted,and the influence mechanism of tool wear on the residual stress distribution of machined surface was analyzed.Based on the theory of fatigue mechanics and mathematical statistics,the mathematical model for difference of stress dispersion and fatigue life was established. The rotating and bending tests were carried out on the standard parts after cutting process for the workpiece. The influence of tool wear on fatigue life was revealed by fracture surface morphology and fatigue life study. The results provide theoretical support for control of residual stress and the fatigue property of the machined surface under the actual working conditions.

Enhancement of wear and ballistic resistance of armour grade AA7075 aluminium alloy using friction stir processing

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys,7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant Mo S2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.

Effects of Heat Treatment on Hardness and Dry Wear Properties of a Semi-Solid Processed Fe-27 wt pct Cr-2.9 wt pct C Cast Iron

EfFects of heat treatments on hardness and dry wear properties of a semi-solid processed Fe-26.96 wt pct Cr- 2.91 wt pct C cast iron were studied. Heat treatments included tempering at 500℃, destabilisation at 1075℃ and destabilisation at 1075℃ plus tempering at 500℃, all followed by air cooling. Electron microscopy revealed that, in the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M7C3 carbide was found as radiating clusters mixed with directional clusters. Tempering did not change the microstructure significantly when observed by scanning or transmission electron microscopy. Destabilisation followed by air cooling led to a precipitation of secondary M23C6 carbide and a transformation of the primary austenite to martensite. Precipitation behaviour is comparable to that observed in the conventionally cast iron. Tempering after destabilisation resulted in a higher amount of secondary carbide precipitation within the tempered martensite in the eutectic structure. Vickers macrohardness and microhardness in the proeutectic zones were measured. Dry wear properties were tested by using a pin-on-disc method. The maximum hardness and the lowest dry wear rate were obtained from the destabilisation-plus-tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.

Interspinous Process Implants Causes Wear of the Spinous Processes in Patients Treated for Spinal Stenosis—An Experimental Biomechanical Study with Comparison to Clinical Cases

There are few biomechanical studies on Interspinous Process Implants (IPD);however none investigate the amount of wear on spinous processes. Therefore the objective of the present study was to investigate the effect of repetitive loading of the IPD Aperius on the spinous processes in a biomechanical porcine model. For comparison, three patients treated surgically with the same device have been followed for one to two years clinically and with image analyses (X-rays, MRI, CT-scans). Four lumbar spines from 6 months old porcine were divided into seven segments, which received IPD. The segments were exposed to 20,000 cyclical loads. Afterwards the deformation (wear) of the segments was registered. The wear of the spinous processes was measured in mm on a following CT-scan. Additionally, the wear of the ex-vivo was compared to that of the spinous processes investigated by CT-scans or X-ray in three patients treated surgically with the same interspinous implant. The mean maximal deformation of porcine specimens was 1.79 mm (SD 0.25) with the largest deformation occurring in the first quarter of the loading (<5000 cycles). The mean wear of the spinous processes after loading was 6.57 mm. A similar level of wear (mean 12.7 mm) of the spinous processes was detected in the patients. The Aperius IPD creates significant wear on the spinous processes in an experimental biomechanical study. Similar wear of the spinous processes is also present in patients treated with the same device post-operatively. How these findings influence the short and long term result of this implant device remains to be investigated in further biomechanical as well as clinical studies. For future development of this type of devices a proper selection of materials and design is essential to minimize wear effects on the spinous processes and thereby increases the possibilities for the devices to function as suggested.

Microstructure,mechanical properties,and wear resistance of VCp-reinforced Fe-matrix composites treated by Q&P process

A quenching and partitioning(Q&P) process was applied to vanadium carbide particle(VCp)-reinforced Fe-matrix composites(VC-Fe-MCs) to obtain a multiphase microstructure comprising VC, V8 C7, M3 C, α-Fe, and γ-Fe. The effects of the austenitizing temperature and the quenching temperature on the microstructure, mechanical properties, and wear resistance of the VC-Fe-MCs were studied. The results show that the size of the carbide became coarse and that the shape of some particles began to transform from diffused graininess into a chrysanthemum-shaped structure with increasing austenitizing temperature. The microhardness decreased with increasing austenitizing temperature but substantially increased after wear testing compared with the microhardness before wear testing; the microhardness values improved by 20.0% ± 2.5%. Retained austenite enhanced the impact toughness and promoted the transformation-induced plasticity(TRIP) effect to improve wear resistance under certain load conditions.

Intelligent Identification of Wear Mechanism via On-line Ferrograph Images

Condition based maintenance（CBM） issues a new challenge of real-time monitoring for machine health maintenance. Wear state monitoring becomes the bottle-neck of CBM due to the lack of on-line information acquiring means. The wear mechanism judgment with characteristic wear debris has been widely adopted in off-line wear analysis; however, on-line wear mechanism characterization remains a big problem. In this paper, the wear mechanism identification via on-line ferrograph images is studied. To obtain isolated wear debris in an on-line ferrograph image, the deposition mechanism of wear debris in on-line ferrograph sensor is studied. The study result shows wear debris chain is the main morphology due to local magnetic field around the deposited wear debris. Accordingly, an improved sampling route for on-line wear debris deposition is designed with focus on the self-adjustment deposition time. As a result, isolated wear debris can be obtained in an on-line image, which facilitates the feature extraction of characteristic wear debris. By referring to the knowledge of analytical ferrograph, four dimensionless morphological features, including equivalent dimension, length-width ratio, shape factor, and contour fractal dimension of characteristic wear debris are extracted for distinguishing four typical wear mechanisms including normal, cutting, fatigue, and severe sliding wear. Furthermore, a feed-forward neural network is adopted to construct an automatic wear mechanism identification model. By training with the samples from analytical ferrograph, the model might identify some typical characteristic wear debris in an on-line ferrograph image. This paper performs a meaningful exploratory for on-line wear mechanism analysis, and the obtained results will provide a feasible way for on-line wear state monitoring.

Optimization of image capturing method of wear particles for condition diagnosis of machine parts

Wear particles are inevitably occurred from moving parts, such as a piston-cylinder made from steel or hybrid materials. And a durability of these parts must be evaluated. The wear particle analysis has been known as a very effective method to foreknow and decide a moving situation and a damage of machine parts by using the digital computer image processing. But it is not laid down to calculate shape parameters of wear particle and wear volume. In order to apply image processing method in a durability evaluation of machine parts, it needs to verify the reliability of the calculated data by the image processing and to lay down the number of images and the amount of wear particles in one image. In this work, the lubricated friction experiment was carried out in order to establish the optimum image capture with the 1045 specimen under experiment condition. The wear particle data were calculated differently according to the number of image and the amount of wear particle in one image. The results show that capturing conditions need to be more than 140 wear particles in one image and over 40 images for the reliable data. Thus, the capturing method of wear particles images was optimized for condition diagnosis of machine moving parts.

Dimensional Description of On-line Wear Debris Images for Wear Characterization

As one of the most wear monitoring indicator, dimensional feature of individual particles has been studied mostly focusing on off-line analytical ferrograph. Recent development in on-line wear monitoring with wear debris images shows that merely wear debris concentration has been extracted from on-line ferrograph images. It remains a bottleneck of obtaining the dimension of on-line particles due to the low resolution, high contamination and particle’s chain pattern of an on-line image sample. In this work, statistical dimension of wear debris in on-line ferrograph images is investigated. A two-step procedure is proposed as follows. First, an on-line ferrograph image is decomposed into four component images with different frequencies. By doing this, the size of each component image is reduced by one fourth, which will increase the efficiency of subsequent processing. The low-frequency image is used for extracting the area of wear debris, and the high-frequency image is adopted for extracting contour. Second, a statistical equivalent circle dimension is constructed by equaling the overall wear debris in the image into equivalent circles referring to the extracted total area and premeter of overall wear debris. The equivalent circle dimension, reflecting the statistical dimension of larger wear debris in an on-line image, is verified by manual measurement. Consequently, two preliminary applications are carried out in gasoline engine bench tests of durability and running-in. Evidently, the equivalent circle dimension, together with the previously developed concentration index, index of particle coverage area （IPCA）, show good performances in characterizing engine wear conditions. The proposed dimensional indicator provides a new statistical feature of on-line wear particles for on-line wear monitoring. The new dimensional feature conveys profound information about wear severity.

Improvement in Tribological Properties of Surface Layer of an Al Alloy by Friction Stir Processing

An innovative technique, friction stir processing (FSP) was employed to modify the surface layer of Al5083 alloy. The FSP passes of 1 to 4 were applied on alloy samples. The processed samples were subjected to microstructural analysis and dry sliding wear test. FSP resulted in microstructural refinement and improvement in wear resistance of Al5083. Moreover, the results indicated that the more number of FSP passes were found to be more effective in improvement of wear resistance, due to more microstructural refinement. It was also found that the load bearing capacity of samples significantly improved with increasing the number of FSP

Influence of Microstructure and Experimental Parameters on Mechanical and Wear Properties of Al-TiC Surface Composite by FSP Route

Surface properties decide the fatigue, wear and corrosion behavior of a material. Hence their performance can be improved by surface modifications. Friction Stir Processing (FSP) is a promising technique to develop surface composite. The aim of the present study is to develop defect free surface composite of Al 5083 alloy reinforced with TiC particles and investigate the particle distribution in the matrix, mechanical properties and wear behavior of the composites. Microstructural observations were carried out by using optical and scanning electron microscopy (SEM). The microstructural studies revealed that distribution of particles were more uniform in samples subjected to double pass than the single pass FSP. The microhardness profiles along top surface and across the cross section of the processed samples were evaluated. The average hardness along the top surface was found to increase by 27.27%, as compared to that of the base metal (88Hv). The particles were incorporated maximum average depth about 250μm in the surface composite. The slurry erosion tests revealed that the wear rate was highly reduced in case of double pass FSP samples as compared to base metal and single pass FSPed

Experimental study on laser shock processing of brass

Laser shock processing （LSP） is a new surface treatment technique for improving hardness, wear resistance, and fatigue. In this paper, basic theories were introduced and the influence of laser pulse intensity on the laser shock processing of brass specimens was investigated by experiments. Microhardness, roughness, microstructure, wear resistance, friction coefficient evolution, and residual stress were examined with different laser pulse intensities of LSP. The results show that the microhardness increases after LSP treatment, and the higher the pulse intensity, the higher the microhardness. Though the microstructure shows no remarkable change, the roughness and wear resistance increase with the increase in pulse density. Laser shock processing has great potential as a means to improve the mechanical properties of components.

Wear behaviors and lubrication medium of TiC/Al_2O_3 ceramic wire drawing dies

The suitable test equipment for wire-drawing was designed. Wire-drawing tests were carried on with this equipment for TiC/Al2O3 ceramic wire-drawing die. Effect of lubrication medium and drawing velocity on the drawing force was investigated. The wear mechanisms of the ceramic drawing dies were investigated. Worn bore surfaces of the ceramic drawing dies were examined by scanning electron microscopy. The results show that lubricant media have great influence on the drawing force. The drawing force is the smallest when a grease lubricant is used. But alteration of drawing velocity has scarcely any influence on the drawing force. Detailed observations and analyses of the die wear surface reveal that the most common failure of the ceramic drawing die is the wear in the invariable zone and bearing zone owing to the greater press stresses. Abrasive and adhesive wear are found to be the predominant wear mechanisms for ceramic drawing die.

高速激光熔覆工艺参数对Fe基合金熔覆层组织与耐磨性能的影响

采用高速激光熔覆技术在27SiMn钢筒形件表面制备Fe基合金熔覆层,对不同工艺参数下该熔覆层的组织形貌、显微硬度和摩擦磨损性能进行分析,探究高速激光熔覆工艺参数对熔覆层组织、硬度及耐磨性的影响。结果表明:不同工艺参数下,熔覆层内部无孔洞、裂纹等缺陷,与基体均形成有效的冶金结合;熔覆层厚度随激光功率的增加先上升后下降;随送粉速率的增加而增加,熔覆层显微硬度、耐磨性随激光功率、送粉速率的增加呈增加的趋势,在实验参数范围内,功率为3000 W、送粉速率为28 rad/min时为最优参数。

Evaluation of Wear and Corrosion Properties of AA6061/TiB₂Composites Produced by FSP Technique

Aluminum alloys are used frequently in aerospace and ship building industry. Due to poor wear and corrosion resistance, conventional aluminum alloys are replaced by metal matrix composites (MMC). Aluminum alloy matrix reinforced with ceramic particles (TiB2) has importance in industry where components slide each other. The main task is to produce MMCs with low cost effective way to meet the requirement. In this study, an attempt is made to produce AA6061/TiB2 MMCs with different volume fractions of ceramic particles using friction stir processing technique. The dry sliding wear behavior of composites was investigated using pin on disc method. The lowest wear resistance has obtained for 8% composite. The corrosion of composites was analyzed by salt spray method. It was found that wear and corrosion resistance was increased with increase of reinforcement which was higher for 8% composite.

基于超声强化研磨加工的GH4099合金耐磨服役性能提升研究

GH4099合金具有优异的高温热稳定性、高温力学性能和高温抗蠕变性能,用于航空发动机涡轮盘和涡轮叶片的制造,常处于高温、重载、高频的工作环境,但因耐磨服役性能差导致其使用寿命较短。通过超声强化研磨加工技术对GH4099合金分别进行0、3、6、9 min的加工,实现其耐磨服役性能提升。采用超声强化研磨加工技术对GH4099合金板表面进行不同时间的加工处理,并对加工前后的截面显微硬度、金相组织以及表面形貌进行分析。同时,通过往复式摩擦磨损试验对加工前后的试样耐磨性能进行对比分析。研究结果表明:随着加工时间的增加,材料表面显微硬度逐渐增大,最大为432.83 HV,比未加工试样增加43.8%。当加工时间为6 min时,GH4099合金试样的摩擦系数为0.47,磨损率为5.78×10^(-14)m^(3)/(N·m),与未加工试样相比,分别降低24.2%、68.59%,表明超声强化研磨可有效提升GH4099合金耐磨服役性能。

Fabrication of in-situ TiC reinforced composite coating via plasma transferred arc process

In this work, the in-situ TiC panicles reinforced composite coating was prepared by plasma transferred arc process on the surface of Q235 steel. Microstructures, phase composition and wear property of the coating were investigated. The results showed that the composite coating consisted mainly of T-Ni, TiC, Cr23C6, Cr7C3, Ni3Si, CrB, Cr5B3 and FeNi3 phases, and was characterized by fine TiC panicles embedded in Ni matrix. The wear resistance of composite coating was significantly improved compared with that of the steel substrate. The wear volume loss of the substrate was 443 mm3, which was about 9 times as that of in-situ TiC particles reinforced composite coating （49 mm3 ）. It is mainly attributed to the presence of chromium carbide particles and in-situ TiC particles and their favorable combination with Ni matrix.

核电厂调节阀阀杆高硬低摩DLC涂层工艺优化研究

通过调整工件偏压和W掺杂靶功率等工艺参数,研究不同工艺对阀杆DLC膜层性能的影响。利用拉曼光谱研究了不同DLC涂层的化学成分和结构,并采用纳米压痕和显微划痕对涂层的力学性能进行了测试。同时,通过摩擦磨损试验评价了复合涂层的摩擦学性能。结果显示,1200V工件偏压下得到的DLC涂层具有更高的硬度和较低的磨损率。W掺杂的DLC涂层附着力更强,但硬度较低,磨损率较高。这项研究为后续制备高硬低摩DLC涂层工艺设计提供参考。

基于VMD-SSA-LSTM考虑刀具磨损的数控铣床切削功率预测模型研究

传统的切削过程功率获取需要基于复杂的切削功率模型且很少考虑刀具磨损的影响,针对此设计了一种基于变分模态分解(VMD)、麻雀搜索算法(SSA)、长短时记忆(LSTM)神经网络的考虑刀具磨损的数控铣床切削功率预测模型,该模型无需解构数控铣床运行过程的能耗机理,基于一次性的历史实验数据即可实现数控铣床切削过程功率的高精度预测。首先,采用人工智能机器视觉技术对刀具磨损图片进行分析处理,获取刀具磨损图像的数字化特征,从而得到刀具最大磨损量;然后,建立基于VMD-SSA-LSTM考虑刀具磨损的数控铣床切削功率预测模型,利用VMD对数控铣床运行数据进行分解,采用SSA算法对LSTM神经网络超参数进行寻优,并将分解出的铣床运行数据分量输入到LSTM神经网络中,接着将每个分量的预测值相加,得到切削功率预测值;最后以面铣加工为例,将所提出的预测模型与BP神经网络、LSTM神经网络和传统模型进行对比分析,验证了所提模型的有效性和优越性。