Investigations on the Effect of Ball Burnishing Parameters on Surface Hardness and Wear Resistance of HSLA Dual-Phase Steels

Surface finish has a vital influence on most functional properties of a component like fatigue life, wear resistance, corrosion resistance, etc. This has given birth to processes such as lapping, honing, burnishing, etc. Burnishing is a fine finishing operation involving the cold working plastic deformation of surface layers to enhance the surface integrity and the functional utility of a component. The present study has been carried out to establish the effect of burnishing parameters viz. feed rate, speed, force, ball diameter and lubricant on surface hardness, and wear resistance of HSLA dual-phase steel specimens. The result indicates that burnishing parameters have significant effect on the surface hardness and wear resistance.     

强化研磨微纳加工参数对轴承套圈滚道表面硬度的影响

目的 探明不同加工参数对加工表面平均硬度的影响规律。方法 用强化研磨微纳加工技术对6012深沟球轴承内圈滚道表面进行强化处理,通过设置不同的喷射压力、加工时间、喷射角度及钢珠配比获得加工试样。采用洛氏硬度计分别检测加工前后套圈滚道表面硬度,并分析其随各参数变化的规律。结果 加工时间为5 min,喷射角度为45°,喷射压力为0.4～0.6 MPa时,表面硬度随喷射压力的增大而增大,0.6 MPa后维持在HRC61.60附近;喷射压力为0.6 MPa,喷射角度为45°,加工时间为1～5 min时,表面硬度及其增量随时间增加而增大,其后在HRC61.50附近徘徊;喷射压力为0.6MPa,加工时间为5min,喷射角度为35°～55°时,试样表面硬度及其增量先减小后增大,喷射角度达50°后,表面硬度达最大值HRC63.45;钢珠配比则对试样表面硬度影响不大,加工所得试样在HRC61.67～HRC61.80之间。结论 试样表面硬度及其增量随喷射压力、加工时间及喷射角度的增加而增加,且受加工时间影响最大。当加工时间为5 min,喷射压力为0.6 MPa,喷射角度为50°时,可获得较高的平均表面硬度。     

Characterization and Failure Analysis of an Automotive Ball Joint

This case study describes the failure analysis of an automotive lower ball joint that fractured under normal driving conditions. Through spectroscopy, the material was determined to be SAE-AISI 5135H steel. The metallographic examination revealed a tempered martensitic structure, and hardness measurements radially across the surface of the cut ball stud suggested that the stud was through hardened. Scanning electron microscopy of the fracture surfaces indicated fatigue as the main failure mechanism. Finite element analysis was used to analyze the performance of the part under a normal loading condition. A detailed fatigue analysis to determine the effect of various loads on the life of the ball joint was completed using three methods: S-N curve approximation using hardness values, S-N approach using Basquin’s equation, and a linear elastic crack-growth model. The cause of failure was determined to be from surface cracks forming in the high stress concentration neck region where the ball and stud are joined. The presence of a small surface flaw in this region was shown to significantly reduce the fatigue life of the ball joint.     

Wear of Tailored Forming Steels

This study investigates the wear behavior of additively welded cladding layers on less wear-resistant base materials using plasma-transferred arc welding and laser hot-wire cladding. The cladding layers are made from atomized AISI 52100, AISI 5140, and a stainless steel with (0.52 wt% C, 0.9 wt% Si, 14 wt% Cr, 0.4 wt% Mo, 1.8 wt% Ni, 1.2 wt% V, bal. Fe) on unalloyed steel AISI 1022M as the base material. The specimens' microstructure and surface hardness are comparable with conventional specimens of monolithic AISI 52100 and AISI 4140, which is used as a reference. Tribometer tests are carried out in ball-on-disk configuration to investigate the wear resistance of the specimen. The multimaterial specimens show comparable wear behavior to their monolithic counterparts, and a good performance of the stainless specimen in pure sliding is proven. These findings suggest that additive manufacturing processes can be used to clad less wear-resistant base materials and achieve high wear resistance, making it possible to exploit the advantages of surface coatings under severe wear conditions.     

PECVD法制备类金刚石薄膜的结构和摩擦学性能研究

采用射频一直流等离子体增强化学气相沉积技术在单晶硅衬底上沉积了类金刚石薄膜。用激光拉曼光谱仪和原子力显微镜对薄膜的结构和表面形貌进行了表征，并用纳米压痕仪测定了薄膜的硬度。用UMT微摩擦磨损试验机考察了薄膜在不同的滑行速度下薄膜的摩擦学性能。结果表明：所沉积的薄膜具有典型类金刚石薄膜的结构特征，薄膜表面光滑致密，硬度较高；薄膜与氧化铝陶瓷球对磨显示出良好的摩擦学性能，随着滑行速度的增加，薄膜的摩擦系数单调降低，但磨损寿命先增加后降低。     

Non-firing ceramics: Effect of adsorbed water on surface activation of silica powder via ball milling treatment

“Non-firing” ceramics have recently attracted much attention because many functional ceramics can be achieved by this method without the sintering process. The underlying idea of this method is to activate the surface of the particles by ball milling. In this study, the effect of adsorbed water on the surface of raw silica powder was investigated. Amorphous silica powder was mechanically treated by a rotating ball mill system and the surface activity of the raw and treated silica powders was measured based on the water adsorbed volume on the powder surface. The results showed that the surface activity of the silica powder increased with the increasing adsorbed water volume on the surface of the silica powder. In addition, better mechanical properties evaluated by the Vickers hardness test were achieved for the silica with more water adsorbed on its surface. The effect of milling energy and ball to powder ratio on activation of the silica was also investigated.     

满滚子轴承滚柱脱落与掉块原因分析

某厂生产的满滚子轴承仅使用5 d,其滚柱表面就发生了脱落与掉块失效。采用宏观分析、金相检验、化学成分分析和硬度检测等方法对滚柱表面脱落与掉块的原因进行了分析。结果表明:滚柱回火不充分、表面渗碳层硬度梯度变化较大、心部显微组织不均匀以及心部硬度偏低是导致滚柱表面脱落与掉块的主要原因。     

Tribological Properties of Mo-N Hard Coatings on Ti6Al4V by Double Glow Discharge Technique

Mo-N hard coatings on Ti6Al4V were formed using double glow discharge technique. The fundamental coating properties, such as the phase, hardness and elastic modulus were investigated. The tribological performances of the coatings in dry wear condition were studied by means of ball-on-disc wear machine. The experimental results showed that the thickness of the Mo-N hard coating was about 10 µm. The coating was single fcc γ-Mo2N phase with (200) preferred orientation. The hardness and the elastic modulus of the coating was 13.80 GPa and 261.65 GPa respectively. The surface treatment enhanced the hardness and elastic modulus of the surface of Ti6Al4V base greatly. With GCr15 slider ball, the friction coefficient of the Mo-N hard coating was in the range of 0.56~0.65 at the steady state. Though the coating did not show friction reducing effect, it improved the wear resistance of Ti6Al4V greatly.     

燃气轮机滚珠轴承失效分析

某型船用主动力系统滚珠轴承在试车过程中发生滚珠断裂。采用化学成分分析、硬度测试和金相检验等方法对断裂的滚珠进行了分析。结果表明，该滚珠的材料硬度偏高，不符合订货技术要求；同时组织中存在超标的脆性夹杂物，这些均引起材料的缺口敏感性，最终导致滚珠在运行过程中发生脆断。     

Application of a diamond spherical indentor with a large curvature for evaluating the hardness of very hard steel

Conclusions It is possible to extend the hardness-number measuring method represented by (1) to very hard steel, which cannot be tested with a normal ball tip, by applying when necessary relatively small loads to diamond ball indentors with a large curvature. It is possible to lower considerably the maximum hardness for which the above technique is applicable by decreasing the angle at the vertex of the cone and the indentation force. Materials whose hardness is below the indicated limit should be tested with normal loads and ball diameters. Thus, it is possible by means of a ball probe and the new hardness number to evaluate the hardness of all steels, from the very soft to the very hard, and to obtain a hardness number read off the same scale. This property of the technique is of great practical importance [6].     

The Effect of Pulsed Magnetic Treatment of Nitrided Steels for Wear Resistance

Surface engineering approach to increase surface properties such as wear resistance performed by pulsed magnetic treatment of nitrided steels was studied. Selected steel surfaces were treated by pulsed magnetic treatment and plasma ion nitriding with different optimized process parameters. The obtained microstructures were examined to study the influence of magnetic treatment on ion nitriding. SEM, AES, microhardness measurements, and image analyser were used to characterize the surface and interface. The results of this study show that pulsed magnetic treatment reduces residual stresses on the surface, improves the bonding of deposited nitride layers to substrate, influences the nitride layers, case depth, and surface hardness formation and increases the wear resistance.     

Si_3N_4陶瓷球轴承的检验方法

通过分析国内外陶瓷球检测状况 ,结合国内研制和生产工艺 ,确定了能表征陶瓷球质量特征的检验项目 ,即化学分析、密度、断裂韧性、表面缺陷、硬度、压碎强度、孔隙度、显微组织等。提出了陶瓷毛坯球的材质性能、制造质量和显微组织等检验方法。对陶瓷球的研制和生产起到质量控制作用 ,为陶瓷球的质量检验标准的制定提供了依据。     

Critical stresses and strains at the spall edge of a case hardened bearing due to ball impact

Short spall propagation times of failing main shaft ball bearings of aircraft engines are a serious safety concern for single engine aircraft. Bearing designers would like to understand the impact of four variables namely (i) ball material density, (ii) subsurface residual stress, (iii) gradient in yield strength with depth (case hardening), and (iv) raceway surface hardness/yield strength that are thought to affect spall propagation. Extensive spall propagation experiments have been conducted at AFRL, Ohio in the past few years to address this issue. However, a detailed mechanistic analysis of these experiments has not been performed. This work presents an elastic–plastic finite element (FE) model that simulates a ball impacting a spall edge to determine the relative contributions of the four material variables on spall propagation. The magnitude and extent of damage of the spall edge material is determined based on critical stresses and plastic strains induced by the ball impact. The results indicate that the influence of ball density is greatest on inducing damage at the impacted spall edge when compared to the other three properties, which also agrees with the hybrid bearing spall propagation tests conducted at AFRL.     

渗硼对钢铁表面组织与性能影响的研究现状

渗硼是一种应用广泛的表面化学处理技术.详细介绍了渗硼对钢铁组织和性能的影响,主要包括钢铁渗硼后的组织、硬度、耐磨性、耐蚀性和抗氧化性等方面的研究,并提出了渗硼研究存在的问题及今后的研究方向.     

Lubrication characteristics of nano-oil with different degrees of surface hardness of sliding members

In this study, the lubrication characteristics of sliding members were compared with the changes in the hardness of friction surfaces and the application of nano-oil. The materials of the specimens were gray cast iron (AISI 35 and AISI 60) and nickel chromium molybdenum steel (AISI 4320). The friction coefficients and the temperature variations of the frictional surfaces were measured with a disk-on-disk tribotester under a fixed rotation speed. The friction surfaces were observed with a scanning electron microscope (SEM). The friction coefficients of the plate surface increased as the hardness difference increased. The friction coefficient after the lubrication with nano-oil was less than that after lubrication with mineral oil. This is because a spherical nanoparticle plays the role of a tiny ball bearing between the frictional surfaces that improve the lubrication characteristics.     

Gradient Microstructure and Properties of Surface Mechanical Attrition–Treated AZ91D Alloy: An Effect of Colliding Balls Velocity

The surface properties of the AZ91D alloy are altered using surface mechanical attrition treatment (SMAT), a promising method of severe surface deformation, where the role of process parameters is crucial. In this study, specimens are SMATed using ≈3 and ≈10 m s⁻¹ ball velocities (maintaining a constant percentage coverage). The SMATed specimens show higher twin density near the surface, which is reduced gradually, and twin thickness is increased with increasing depth. Further, high-velocity balls cause more twin density and better grain refinement (≈32 nm grain size at the surface). The higher ball velocity helps form a considerably thicker gradient layer (≈3500 μm) with higher hardness (≈1.98 GPa) and compressive residual stress (≈281 MPa) within a shorter SMAT duration (≈10 min). Ball velocity also influences nanomechanical properties such as nanohardness, creep resistance, strain rate sensitivity (SRS), etc. The non-SMATed alloy's SRS is about 0.037–0.040. The gradient microstructure affects SRS. The SRS value near the SMATed surface (where the reduced grain size plays a dominating role) is about 0.018–0.027; however, it drops suddenly to ≈0.01 (with a slight increase in depth), and subsequently, it rises with an increased distance in the SMATed layer (where twins play a dominating role).     

Ultrasonic-assisted ball burnishing of aluminum 6061 and AISI 1045 steel

In the present work, experimental study was carried out to enhance the surface properties of aluminum 6061 and AISI 1045 steel plates by ultrasonic-assisted ball burnishing process. Full factorial experimental design was utilized here to find the effect of ultrasonic vibration, feed rate, and pass number on surface roughness and hardness. The results were discussed according to interaction effect of process factors for different material. It is found from the results that for conventional burnishing process, the highest surface hardness is attained at 5000?mm/min feed rate and 5 pass number, while for ultrasonic-assisted burnishing, the highest hardness is attained at 1000?mm/min feed rate and 5 pass number. On the other hand, it is found from the results that exerting ultrasonic vibration significantly enhances the hardness value and hardened depth. Also, it is found that irrespective of type of operation and material, increase in feed rate causes higher roughness, whereas increase in pass number causes reduction in roughness. Furthermore, surface roughness of ultrasonic-assisted burnishing is lower than that of conventional burnishing process. This enhancement is due to the association of both static and dynamic loading in ultrasonic-assisted burnishing process that causes microstructure modification and limits the elastic recovery of the surface.     

The effect of salt bath cementation on mechanical behavior of hot-rolled and cold-drawn SAE 8620 and 16MnCr5 steels

In this study, the effect of salt bath cementation on mechanical behavior of SAE 8620 and 16MnCr5 cementation steels, which are widely used in industry, was investigated. The experiments were carried out with hot rolled and cold rolled specimens. The cementation processes were performed in NaCN salt bath at 920 °C temperature for 1, 2, 3 and 4 h. Abrasive wear tests of specimens were conducted with Wolfram Carbide (WC) ball for 1 h. After cementation processes, a martensite phase on the surface of specimens was confirmed by X-ray diffraction analysis. After cementation processes carried out with different times, a different surface hardness and effective cementation depth values were obtained. Experimental results showed that an effective cementation depth increased with increasing the cementation time. Wear tests showed that the wear resistance of specimens increased by the cementation processes. Experimental results revealed that the surface hardness of specimen affects the wear resistance of specimens.     

粉末冶金制备工艺对TiC增强高铬铸铁基复合材料性能的影响EI北大核心CSCD

采用高能球磨和真空烧结的方法制备TiC增强高铬铸铁(HCCI)基复合材料。利用SEM,DSC等方法对不同球磨时间的粉末进行分析,研究不同烧结温度对高铬铸铁基复合材料的显微组织、硬度及密度的影响,比较相同工艺下复合材料与高铬铸铁材料的耐磨性。结果表明:球磨12 h后的粉末颗粒大小趋于稳定,粉末活性提高,烧结性能改善,烧结试样中TiC均匀地分布在基体中。随着烧结温度的升高,复合材料内部晶粒逐渐长大,密度和硬度逐渐提高。在1280℃超固相线液相烧结的条件下烧结2 h后,致密度达94.17%,硬度和抗弯强度分别为49.2HRC和980 MPa。在销盘磨损实验中复合材料的耐磨性为单一高铬铸铁材料的1.52倍,磨损机制为磨粒磨损+轻微氧化磨损。     

Tribological properties of polymers PI,PTFE and PEEK at cryogenic temperature in vacuum

The effects of temperature, sliding speed and load on the tribological properties of polyimide (PI), polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK) at cryogenic temperature in vacuum were investigated using a ball-on-disk tribometer. At cryogenic temperature, polymers show higher hardness which results in decreasing contact area between the friction pairs. Moreover, the real surface area in contact between steel ball and polymer disk determines the friction coefficient instead of the formation and adhesion of the transfer film. Thus, the friction coefficients at cryogenic temperatures are lower than at room temperature. On the other hand, wear rates of the three polymers decrease as temperature decreases since molecular mobility and migration are limited at cryogenic temperatures. For the visco-elasticity of PI, PTFE and PEEK, the friction coefficients fall as the load increases.