Zr离子注入对NiTi形状记忆合金表面硬度和耐磨性影响

研究了Zr离子注入参数（注入剂量和注入电流）对NiTi形状记忆合金表面成分、形貌、硬度和耐磨性的影响.发现Zr离子注入后,Zr离子浓度在NiTi合金表面呈高斯分布,同时降低了合金表面的Ni含量.Zr离子注入后合金表面形貌出现沟槽结构,合金外表层纳米硬度、杨氏模量和显微硬度明显提高.摩擦磨损实验结果表明,Zr离子注入降低了NiTi合金初始摩擦因数,显著延长了维持初始低摩擦因数的时间,同时使磨痕的宽度和深度分别减小了30%~50%和28%~50%.因此,选择适当的注入参数可以使NiTi合金获得最佳的耐摩擦磨损性能.      

Experimental Analysis on the Frictional Behaviour of Drawbeads in Sheet Metal Forming

In sheet metal forming, drawbeads are commonly used to control uneven material flow, which may cause defects such as wrinkles, fractures, surface distortion and springback. Although friction may not directly change the limiting strain of steel sheets, the tribological conditions in the contact zone between the sheet surface and the tool surface play an important role in determining the limits of the forming process. Friction in the drawbead contact zones affects the flow of the material in the tool and is used deliberately to control the stamping process. Therefore in this study, the frictional behaviour of drawbeads is experimentally investigated by the drawbead friction test. To characterize the effect of processing variables on the friction coefficients, tests are performed for various sheets, lubricants and bead materials suffering different surface treatments. The results obtained from the drawbead friction test show that the friction and drawing characteristics of deforming sheets were strongly influenced by the strength of sheet, viscosity of lubricant and hardness of bead surface.     

Effects of laser-shock processing on the microstructure and surface mechanical properties of hadfield manganese steel

The effects of laser-shock processing (LSP) on the microstructure, hardness, and residual stress of Hadfield manganese (1 pct C and 14 pct Mn) steels were studied. Laser-shock processing was performed using a Nd: glass phosphate laser with 600 ps pulse width and up to 120 J/pulse energy at power density above 10¹² W/cm². The effects of cold rolling and shot peening were also studied for comparison. Laser-shock processing caused extensive formation of ε hexagonal close-packed (hep) martensite (35 vol pct), producing up to a 130 pct increase of surface hardness. The surface hardness increase was 40 to 60 pct for the shot-peened specimen and about 60 pct for the cold-rolled specimen. The LSP strengthening effect on Hadfield steel was attributed to the combined effects of the partial dislocation/stacking fault arrays and the grain refinement due to the presence of the ε-hcp martensite. For the cold-rolled and shot-peened specimens, the strengthening was a result of ε-hcp martensite and twins with dislocation effects, respectively. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than LSP.     

钛含量对铜基粉末冶金摩擦材料摩擦磨损性能的影响

采用粉末冶金方法制备铜基摩擦材料,研究钛的添加量对材料的摩擦磨损性能的影响。结果表明:随着钛质量分数由3%增加到12%,铜基摩擦材料的相对密度提高,硬度增加。钛的添加导致晶格畸变,材料硬度提高。随着摩擦速度增加,材料的摩擦因数减小。钛添加到铜基摩擦材料中,降低了铜基摩擦材料的摩擦因数和磨损量,原因在于钛提高了材料的硬度,增加了表面微凸体强度,减少了犁削程度,从而降低了摩擦面的损伤程度,提高了材料的耐磨性。     

Effect of Oxide Content on the Tribological and Physicomechanical Properties of Filled Polytetrafluoroethylene

The effect of the nature and the amount of oxide fillers on antifriction properties of polytetrafluoroethylene under dry friction conditions with different loads and slow sliding rates is studied. It is established that oxides with a high hardness increase the friction coefficient and reduce the wear resistance of filled polytetrafluoroethylene, but oxides with a low hardness do not give rise to an increase in friction coefficient for polytetrafluoroethylene with a marked increase in its wear resistance, and this is connected with formation of a separating layer at the surface of the friction pair.     

Room Temperature Case Carburizing of a Ni–Cr–Mo Steel Through Shot Peening/Blasting Techniques

Controlled shot-peening/blasting is an operation which is used largely in the manufacturing industry. An attempt is made to create a case-hardened surface by the shot peening technique on a Ni–Cr–Mo steel. Steel shots with activated carbon powders were introduced at the surface of the samples for different periods of time, i.e. for 5, 10, 15 and 20 min. The microstructure, chemical composition, and hardness were investigated by optical microscopy, SEM, OES, XRF, XRD and micro-Vickers hardness tester, respectively. An effective diffusion of carbon atoms was found in the samples subjected to shot peening for 10 min. and above. However, the hardness values were found to be non-uniform and showed a maximum hardness of 300 HV_0.3 at activated spots. The microstructural studies revealed formation lamellar-shaped cells consisting of nano grains at the shot peened surface. A close observation of these lamellae shows α-ferrite and cementite (Fe₃C) formed by diffusion of carbon into iron at room temperature. XRD results confirmed the formation of Cr₂₃C₆ and Fe₃C by shot peening with activated carbon.     

Peak Friction Behavior of Smooth Geomembrane-Particle Interfaces

An investigation of shear mechanisms at interfaces between particles and relatively smooth materials using contact mechanics and basic friction theory reveals that a combination of sliding and plowing governs dense Ottawa 20∕30 sand∕smooth high density polyethylene geomembrane peak interface shear behavior. Contact area and the corresponding shear resistance during sliding increase at a slower rate than the applied normal stress, resulting in a decreasing friction coefficient and flattening of the peak strength envelope. Plowing of soil grains results in an increasing peak friction coefficient with increasing normal stress and can produce an upward curvature of the strength envelope above a critical stress level. Plowing is primarily controlled by the relative hardness of the interface materials and by grain shape with angular particles exhibiting plowing in all normal stress ranges, whereas nearly perfect spheres exhibit only sliding. High surface hardness is shown to constrain shear behavior to a sliding mode with little contribution from plowing. These findings are consistent with results reported in the tribology literature.     

Microstructure Evolution of Surface Gradient Nanocrystalline by Shot Peening of TA17 Titanium Alloy

A surface gradient nanocrystalline structure (SGNS) was obtained by shot peening (SP) on the TA17 near α titanium alloy to improve its surface properties. The effect of shot peening time was investigated by characterizing the grain size of the surface nanocrystalline layer, the thickness of the severe plastic deformation (SPD) layer, the microstructure evolution of the SGNS and the hardness change. The experimental results show that the grains of TA17 titanium alloy can be refined to a nano-scale of about 22 to 26 nm when shot peened at 0.6 MPa pressure for 5 to 10 minutes. The thickness of the SPD layer increases from 55 to 88 μm with the SP duration from 5 to 10 minutes and tends to be saturated afterward. The SGNS is composed of a surface nanocrystalline layer and a transition layer. During the SP treatment, the coarse grains are first divided into small blocks by intersection of twins, then dislocation walls, dislocation tangles and dislocation bands lead to the formation of low-angle grain boundaries, which subdivide the subgrains into a finer scale until nanograins with a stable size are obtained. The topmost surface hardness can be improved significantly to twice the hardness of the matrix due to both grain refinement and work-hardening.

     

Friction Stir Processing of Aerospace Aluminum Alloy by Addition of Carbon Nano Tube

Aluminum 7075 is an aerospace alloy that has high strength to weight ratio and used most commonly in aeronautic structures. However, low surface properties such as poor wear resistance and surface hardness are the main weaknesses that limit its application in other areas of manufacturing. In the present work an attempt was made to fabricate aluminum based surface nano-composite reinforced with carbon nano tube (CNT) by means of single pass friction stir processing. Firstly, Microstructural evolution, tensile properties, hardness, wear rate and friction coefficient of fabricated surface composite was compared with pure friction stir processed metal and base material. Hereafter, parametric study based on response surface methodology was carried out to find the effect of tool rotary speed, feed rate and amount of MWCNT on tensile strength and wear rate. Optimization based on desirability approach function was also performed to find optimal parameter setting achieving maximum strength and minimum wear rate, simultaneously. The results revealed that the CNT particles significantly homogenized the microstructure of the composite, enhanced tensile properties and hardness and reduced the wear rate and friction coefficient in sliding test. By performing optimization through RSM, it was found that selection of 1250 RPM tool rotary speed, 40 mm/min feed rate and 0.6 g CNT weight caused 20% improvement in tensile strength and wear rate of fabricated composite when compared with base material.     

Al_2O_3含量对铜基粉末冶金摩擦材料摩擦磨损性能的影响

采用粉末冶金方法制备铜基摩擦材料,研究Al_2O_3的添加量对材料的摩擦磨损性能的影响。结果表明:Al_2O_3对材料摩擦磨损性能的影响与摩擦速度密切相关;随着Al_2O_3含量增加,材料的摩擦因数提高,密度降低,硬度增加,磨损量先减小后增大,Al_2O_3质量分数为9%时,复合材料的摩擦因数较高且稳定,磨损量最小。不含Al2O3的材料摩擦表面出现大量凹坑,磨损严重,随着Al_2O_3含量提高,凹坑数量减少,弥散分布的Al_2O_3粒子能强化基体表面强度,从而导致材料磨损量降低。     

Behaviour of Longitudinal Cracks on Slab Surfaces in V‐H Rolling Processes

The behaviour of longitudinal cracks on slab surfaces in multi‐pass vertical‐horizontal rolling processes was simulated by the finite element method (FEM). The influence of friction coefficients and fillet radii of grooved edge rolls on the closure and growth of cracks were analysed in regard to crack shape and crack length elongation ratio. The results indicate that the crack width increases both with increasing friction coefficient and with increasing fillet radii of the grooved edger rolls; the crack length increases as the fillet radii increase in V₁ and H₁ passes, and decreases as the fillet radii increase in V₂ ~ H₃ rolling. Moreover, the cracks become longer under a higher friction coefficient. Experiments of the behaviour of longitudinal cracks on slab surfaces in multi‐pass V‐H rolling processes were investigated taking lead as model material for the hot rolling of steel. The calculated results showed similar deformation variations compared to the experimental ones.     

Assessment of CpTi Surface Properties after Nitrogen Ion Implantation with Various Doses and Energies

Nitrogen ion implantation is one of the surface modification techniques used for increasing corrosion resistance of commercially pure titanium (CpTi). The nitrogen ion implanted CpTi in various doses markedly changes the corrosion resistance. Still the effect of nitrogen ion implantation on the CpTi at different energies needs to be verified. This study uses different methods to assess the CpTi surface properties after nitrogen ion implantation in various doses and energy. Surface hardness of the CpTi increases with an increase of the dose and decreases with an increase of the energy. The precipitation of the TiN increases with an increase of the nitrogen dose, and no formation of the Ti₂N phase clearly appears. Corrosion resistance of the CpTi specimens can be upgraded to some extent after their surfaces are modified, implanting nitrogen ions at 100?keV by increasing dose. The optimum surface properties of the implanted CpTi are analyzed to contribute to materials science technology.     

New method for measuring and characterisation of friction coefficient at wide range of densities in metal powder compaction

Abstract

In order to investigate the friction behaviour of powder during compaction, a new method has been developed. Compaction is a complicated process and direct and continuous measurement of the coefficient of friction is not easy, because the coefficient of friction varies due to changes in such process parameters as pressure distributions, powder surface deformation etc. In this paper, a new device for measuring the coefficient of friction between metal powder particles in contact with the die wall during compaction is presented. Using the conventional methods for direct measurement of the radial pressure during compaction is very difficult. The new device offers the possibility of investigating the normal pressure on the powder particles directly and continuously by keeping the green density constant. The measurements are performed using strain gauges mounted on the upper punch. The upper punch surface in the new device corresponds to the die wall in a conventional press. The sliding velocity, compaction velocity, normal load and temperature can be monitored and controlled. Measurement of the coefficient of friction at low densities is one of the advantages and possible applications of this apparatus. The investigation shows that the powder compaction is controlled by a combination of powder rearrangement and elastic and plastic deformation of particles. At densities below 4g cm^-3 the dominant process is particle rearrangement. No plastic deformation occurs at such low values of density. At densities above 4·5g cm^-3 the plastic deformation of the powder surface in contact with the die wall seems to be completed and the coefficient of friction is more or less constant.     

Vacuum carburization of 12Cr2Ni4A low carbon alloy steel with lanthanum and cerium ion implantation

As bearing parts, 12 Cr2 Ni4 A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12 Cr2 Ni4 A. However, the traditional carburizing is limited by poor microstructure distribution and low rate of carburizing. The rare earth ion implantation is known to help improving the properties of tribology, corrosion resistance and oxidation resistance of metal. In this article, the RE implantation is employed to assist the carburizing. Lanthanum and cerium ion implantations are initially used to assist 12 Cr2 Ni4 A low pressure vacuum carburization.The microstructure, content of retained austenite, hardness, thickness of layer and carbon diffusion were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD) and Rockwell/Vickers hardness tester, respectively. It was shown that lanthanum and cerium implantations can improve structure of the vacuum carburizing layer, and enhance the uniformity of carbon element distribution on the carburized surface. Meanwhile the RE implantation plays a positive role in promoting the surface hardness and carburized rate. The lanthanum element has more significant effect on surface hardness and content of retained austenite than cerium element. The surface hardness of lanthanum element implanted layer was 62.9 HRC with 9.6% content of retained austenite, while the carburizing rate of cerium implanted layer increased by 12.4%.     

Effects of simultaneous boron and nitrogen implantation on microhardness and fatigue properties of Fe-13cr-15ni alloys

Eight complex austenitic stainless steel alloys based on the composition Fe-13Cr-15Ni-2Mo-2Mn-0.2Ti-0.8Si-0.06C were implanted simultaneously with 400-keV B+ and 550-keV N⁺ ions and were investigated for changes in fatigue properties and surface microhardness. The nearsurface hardness of all eight alloys improved, but the fatigue life of each decreased. These findings were contrary to those obtained in an earlier study using four simple Fe-13Cr-15Ni alloys, where the dual implantation improved fatigue life by up to 250 pct. While unimplanted specimens failed by slip-band crack initiation, it was hypothesized that the dual implantation suppressed slip to the extent that fewer slip-band cracks were initiated and these were subjected to accelerated crack propagation. In addition, grain-boundary cracking was promoted, yielding a lower fatigue life. Support for this hypothesis was obtained by a study of single crystals of Fe-15Cr-15Ni, which were also implanted with B⁺ and N⁺. The dual implantation caused a lower fatigue life due to concentration of slip along a few slip bands to relieve applied stress. Evidence of grain-boundary cracking was obtained using the four simple alloys, which were subjected to triple ion implantation with B⁺, N⁺, and C⁺. The triple implantation decreased the fatigue life of the alloys and caused accelerated growth of fewer slip bands and grain-boundary cracking due to suppression of surface slip bands. This study thus shows the existence of an optimum level of strengthening when multiple ion implantation is used to improve the fatigue properties of alloys.     

High Temperature Tribological Studies on Surface Engineered Tool Steel and High Strength Boron Steel

The popularity of hot sheet metal forming processes in the recent years has necessitated research efforts to improve tool life and control the friction level during hot forming operations. In this work, the tribological properties of tool steel and ultra high strength boron steel (UHSS) pairs at elevated temperatures have been studied by using a special hot sheet metal forming test rig that closely simulates the conditions prevalent in the real process. This test involves linear unidirectional sliding of a preheated UHSS sheet between two tool steel specimens where new workpiece material is continuously in contact with the tool surface. The study is aimed at investigating different surface treatments/coatings applied on either the tool or sheet surface or on both. The results have shown that it is possible to control the coefficients of friction through surface treatments and coatings of the tool and workpiece materials. The application of a coating onto the sheet material has a greater influence on the friction compared to changing the tool steel surface. After running‐in, the investigated tool steel variants show almost similar frictional behaviour when sliding against the same sheet material. Although coating the UHSS sheet reduces friction, it abrades the tool surface and also results in transfer of the sheet coating material to the tool surface.     

复压复烧对烧结减摩Cu-Ti3SiC2导电材料性能的影响

利用粉末冶金技术制备了10%Ti3SiC2颗粒增强Cu基减摩、导电材料。以200,400和500 MPa的压力对烧结试样进行复压,然后复烧,以提高材料的密度。通过测量试样的密度、硬度和电阻率,探索了复压复烧对材料性能的影响,并对试样进行了通电和不通电情况下的摩擦、磨损试验。结果表明,经400 MPa复压复烧后,材料的密度和硬度得到显著提高,密度由7.309 g·cm-3增加至7.712 g·cm-3,而硬度则达到HB 114,导电性能和减摩、抗磨能力也因此得到了改善,摩擦系数有所降低,磨损量减少了68%。与未带电的情况相比,带电时的摩擦因数相对较小,但磨损量则较大。在带电磨损实验过程中,摩擦副的温度升高使样品表面的铜基体部分氧化,并起到了润滑作用,从而降低了摩擦因数。     

钢铁材料表面自身纳米晶化及其应用前景

实现钢铁材料表面自身纳米晶化的主要方法有超声喷丸、高能喷丸和机械研磨处理等。大塑性变形诱发晶粒碎化和应变诱导相变是钢铁表面自身形成纳米晶的主要机制。表面自身纳米晶化能够显著提高钢铁材料的表面强度、硬度、耐磨和耐疲劳性能，在化学热处理和电化学防护方面展示了广阔的应用前景。     

( Tb,Dy) Fe2合金表面离子注入渗氮改性及抗腐蚀性能研究

采用离子注入技术在(Tb,Dy)Fe2稀土超磁致伸缩材料表面引入氮离子进行改性处理,研究了加速电压对材料表面相结构、微观形貌、表面硬度、抗酸碱腐蚀性能及磁致伸缩性能的影响.结果表明:离子注入渗氮后,(Tb,Dy)Fe2合金表面的REFb相分解,生成了REN,α-Fe和Fe8N新相,材料表面微观形貌发生了明显变化,表面硬度明显提高.通过测试极化曲线研究了渗氮前后(Tb,Dy)Fe2合金在不同PH值NaCl溶液中的抗酸碱腐蚀性能,发现pH值相同条件下渗氮处理后(Tb,Dy) Fe2合金的自腐蚀电位Ecorr较渗氮前明显正移且有钝化现象发生.在加速电压140 kV,离子注入剂量5.0×1017 ion.cm -2条件下渗氮处理的(Tb,Dy)F合金,处于20℃,3.5％ NaCl溶液环境中,pH=4时,△Ecorr=0.23413 V; pH =7时,△Ecorr =0.18992 V; pH=10时,△Ecorr =0.01268 V,渗氮处理后(Tb,Dy)Fe2合金的抗酸腐蚀性能明显增强,抗碱腐蚀性能变化不明显.随着pH值的增大,渗氮与未渗氮(Tb,Dy) Fe2合金的抗腐蚀性能均变差.由于离子注入表面渗氮的渗氮层很薄,渗氮温度很低,渗氮处理没有破坏材料的内部基体结构,因此渗氮后材料渗氮处理没有破坏材料的内部基体结构,其磁致伸缩性能几乎未受影响.研究表明离子注入渗氮是(Tb,Dy)Fe2磁致伸缩材料表面改性的一种有效方法.     

稀土Y离子注入对形成不同类型氧化膜合金的高温抗氧化性能的影响

：研究了稀土Ｙ离子注入对ＦｅＣｒ,ＦｅＣｒＡｌ及ＮｉＣｒ合金高温抗氧化性能的影响。结果表明,对于主要形成Ｃｒ２Ｏ３膜的ＦｅＣｒ和ＮｉＣｒ合金,通过离子注入Ｙ可以明显提高其高温抗氧化性能,但对形成Ａｌ２Ｏ３膜的ＦｅＣｒＡｌ合金,离子注入对合金抗氧化性能没有影响,添加稀土Ｙ则使ＦｅＣｒＡｌ合金抗氧化性能大大提高。分析了氧化前、后氧化膜结构变化,认为早期形成的Ｙ２Ｏ３膜对高温氧化时金属离子的扩散有不同的影响