Mechanical and wear characterization of electroless nickel-boron coatings

Nanocrystalline electroless nickel-boron deposits were synthesized on mild steel (St-37 ASTM A36) substrates and submitted to heat treatment under non-reactive atmosphere to enhance their properties. Their mechanical and tribological properties were investigated by various methods including nanoindentation, Taber wear testing and scratch tests. Their structural properties were also studied.The hardness of the deposits increased from 900 to 1250 hv₂₅ due to optimal crystallization of the nanocrystalline coating while the Taber wear index was halved after heat treatment.The scratch tests resistance of the coatings was good in both as-deposited and heat treated conditions.The mechanisms inducing the modification of the mechanical and tribological properties were discussed and they were linked to the structural state of the material.     

Comparison between nanoindentation and scratch test hardness (scratch hardness) values of copper thin films on oxidised silicon substrates

In this paper we measured for the first time the scratch hardness of copper thin films and compared this with hardness measured from nanoindentation. Copper films with thicknesses in the range 100 nm to 500 nm were deposited by rf magnetron sputtering on silicon substrates. Scratch hardness was determined by CSM™ scratch tester using scratch widths at low loads. The measured hardness values were compared with conventional nanoindentation hardness measurement by CSM™ nanohardness tester. At these low indentation depths there is a good correlation between the scratch hardness and the nanoindentation hardness, with an increase in hardness as the film thickness decreases.     

Microstructure and surface mechanical properties of electrodeposited Ni coating on Al 2014 alloy

The surface of Al 2014 was modified by electrochemical deposition of Ni with an aim to improve the surface mechanical properties of the alloy. The deposition was performed at various values of DC current, potential and time using standard Watt's bath. The samples were heat treated to improve the adhesion and hardness of Ni coatings. Material characterization was performed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction. Microhardness, nanohardness, microscratch and coefficient of friction measurements were undertaken to determine the surface mechanical properties of the electrodeposited Ni coating. Experimental results indicate that electrochemical deposition combined with heat treatment can be used to improve the surface properties of Al alloys.     

A modified scratch test for the mechanical characterization of scratch resistance and adhesion of thin hard coatings on soft substrates

The scratch resistance of coatings and the adhesion between coating and substrate are usually determined in model experiments performed with sharp diamond indenters. These common methods as described for example in EN 1071-3 often fail for the combination of hard coatings on soft substrates due to very small critical loads or no detectable failure modes at all. Hence in the industry a lot of highly subjective and provisional test methods are used. On the one hand, quantitative comparability is difficult with common methods since defects already occur at very small loads for ductile and relative soft substrate materials like plastics. On the other hand, wear of the indenter in contact with hard coatings like pure diamond coatings requires its cost-intensive replacement.In this article a macroscopic tribological–mechanical test method is suggested which uses balls of hardened steel as indenters. A wide scope can be applied for both soft and hard coatings and different substrate materials. By variation of the ball-diameter, the normal contact force and the sliding speed different levels of stress and wear can be induced to analyze the tribological and mechanical behavior between body and counterpart as well as the interface of coating and substrate. To determine scratch resistance close to reality as usual scratch conditions on consumer products are better represented by a small ball than a sharp diamond indenter. Another benefit of the presented test method is the cost saving acquisition of the balls for indentation in very high quality as they are standard parts in the ball bearing industry. For every test on very hard coatings a new ball can be used with the possibility to detect the wear both on the base object and the counterpart. The occurring failure modes of coating and substrate also can be compared with comparatively easy numerical models to verify the results. Additionally to the test concept, first results of different coatings will be presented in this paper and compared with the results of common scratch tests.     

Evolution of deformation and friction during multimode scratch test on TiN coated D9 steel

Three different scratch modes were used to induce deformation in TiN coating deposited on D9 substrate. The consequent surface damage was analyzed using optical and scanning electron microscopy. Main deformation mechanisms found during Progressive Load Scratch Test and Constant Load Scratch Test were cohesive cracking, coating spallation and adhesive failure. However, ductile fracture was induced during Multi Pass Scratch Tests (MPSTs) performed at three different loads. The trend of evolving coefficient of friction was found to be different for three kinds of scratch modes and the evolution of coefficient of friction has been correlated with coating deformation.     

Mechanical properties, corrosion behaviors and microstructures of 7075 aluminium alloy with various aging treatments

The influence of two novel aging treatments, T616 （130 ℃, 80 min ＋ 65℃, 240 h＋130℃, 18 h） and high-temperature pre-precipitation（HTPP） aging （445℃, 30 min＋120℃, 24 h） on the tensile properties, intergranular corrosion, exfoliation corrosion behaviors and microstructures of 7075 AI alloy was studied, which were compared with the T6, T73 and RRA treatments. Fine η＇ precipitate with high density was obtained in the alloy with the T6 and RRA treatments. The η＇ precipitate density in the HTPP aged alloy is decreased due to the formation of coarse particles during the pre-precipitation process at high temperature of 445℃. The 7075-T616 alloy possesses higher precipitate density and whole precipitate volume fraction within the grain than the 7075-T73 alloy, and its whole precipitate volume fraction is even greater than that of the 7075-T6 alloy. Compared with T6 treatment, the RRA, T73, T616 and HTPP aging treatments cause the discontinuous distribution of the η precipitates at the grain boundary, which decreases the intergranular corrosion and exfoliation corrosion susceptibility of the alloy. Meanwhile, the T616 and RRA treatments can keep the high strength of the 7075 AI alloy, but the studied HTPP aging and T73 treatments lower its strength.     

Characterization of mechanical properties of suspension plasma sprayed TiO2 coatings using scratch test

The study aimed at characterizing mechanical properties of TiO₂ coatings obtained by the use of aqueous suspensions of fine rutile and anatase particles onto metal substrates. Thickness of the coatings was found with the use of optical microscope observations of metallographical cross-sections. The coatings morphology was found with scanning electron microscope (SEM) and their phase composition was determined by X-ray diffraction method. The mechanical properties were characterized using scratch test. The test enabled to characterize the adhesion of coatings by determination of critical force necessary to peel off the coatings from the substrate and, on the other hand, to estimate their cohesion by the measurement of the scratch hardness. The hardness was calculated using the width of the scratch and the value of force applied. The design of experiments (DOE) of spraying with the use of a 2³ full factorial plan was applied to rutile powder. The coatings were sprayed onto aluminium substrate. The DOE enabled to find the effects of three principal parameters, i.e. electric power input to plasma, spray distance and suspension feed rate onto coating adhesion expressed by critical force. A preliminary data for anatase powder sprayed with one set of operational parameters onto stainless steel substrate are also shown.     

Abrasive wear resistance of electroless Ni-P coated aluminium after post treatment

Electroless nickel (EN) coatings are recognised for their hardness and wear resistance in automotive and aerospace industries. In this work, electroless Ni-P coatings were deposited on aluminium alloy substrate LM24 (Al-9 wt.% Si alloy) and the effect of post treatment on the wear resistance was studied. The post treatments included heat treatment and lapping with two different surface textures. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and micro-abrasion tester were used to analyse morphology, structure and abrasive wear resistance of the coatings. Post heat treatment significantly improved the coating density and structure, giving rise to enhanced hardness and wear resistance. Microhardness of electroless Ni-P coatings with thickness of about 15 μm increased due to the formation of Ni₃P after heat treatment.     

Formation behaviour of blister in cast aluminium alloy

Abstract

The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus’ high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.     

The influence of surface treatment on filiform corrosion resistance of painted aluminium alloy sheet

Filiform corrosion of AA 5005 H14 aluminium alloy sheet has been investigated. Painted and scribed panels, with different surface treatments, were inoculated in HCl and exposed in a constant humidity cabinet maintained at 40 °C and 75-85% RH for 1000 h. After exposure, the panels were examined by optical and electron microscopy. It is evident that filiform corrosion susceptibility is determined largely by the near-surface microstructure. Heavily deformed layers, comprising oxide-decorated fine grains and dispersoids on as-rolled and mechanically ground alloy surfaces, are readily susceptible to filiform corrosion. Removal of these deformed layers, by caustic etching and acid cleaning, results in a high filiform corrosion resistance. On such surfaces, underfilm corrosion progresses by localized corrosion of the substrate; with comparatively slowly growing filaments propagating by repeated blistering of the overlying lacquer.     

7A41铝合金的力学性能和耐蚀性能

采用常温拉伸性能测试、应力腐蚀性能测试和盐雾腐蚀性能测试方法分别对双级时效态7A41铝合金的力学性能及耐蚀性能进行了测试。采用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)对合金的显微组织、拉伸断口微观形貌进行了表征。结果表明,T6状态下合金的抗拉强度、屈服强度和伸长率分别为505 MPa、474 MPa和16.3%。耐应力腐蚀性能优异,应力腐蚀敏感系数为3.98%,合金的盐雾腐蚀速度为0.0914 mm/y。TEM观察分析表明,Tb态7A41铝合金晶内均匀弥散地分布着纳米级析出相,晶界上分布着大量的非连续析出相,析出相尺寸为20~50 nm,非连续析出相有效地阻碍了合金晶间腐蚀的路径,良好的组织特征保证了合金的综合性能。     

Processing and properties of ultrafine-grain aluminium alloy 6111 sheet

The equal channel angular processing (ECAP) technique has been applied to an automotive aluminium alloy sheet (A6111). The technique utilizes a machine that was specially designed for this purpose at Monash University. It was determined that ECAP is able to refine the grain size of the sheet, diminish the detrimental as-rolled texture components in the sheet and retain an acceptable level of bi-axial ductility such as is required during the automotive forming process. Experiments were carried out on annealed, as-received sheets that were subjected to either one or two passes through the ECAP machine. For the second ECAP pass, the sheet could be processed in the same orientation as the first pass (route A) or it could be rotated 180° about the direction of feeding (route C). It was determined that route A produced marginally improved properties compared to sheet processed via route C, and that due to the frictional heating generated during the second pass, a significant amount of recovery occurred in the sheet such that an improved combination of texture and formability resulted after two passes compared to the same sheet exposed to only a single pass.     

An integrated study on the effect of pre- and post-extrusion heat treatments and surface treatment on the filiform corrosion properties of an aluminium extrusion alloy

The effect of pre- and post-extrusion heat treatments on the filiform corrosion behaviour of a well-known aluminium extrusion alloy AA6063 is studied by a combination of accelerated filiform corrosion exposure tests and potentiodynamic polarisation measurements for four different surface treatments. It is shown that the post-extrusion heat treatment of this AlMgSi alloy can influence the filiform corrosion properties significantly, in particular for the milder surface treatments. In contrast, the relative effect of the pre-extrusion treatment on the filiform corrosion properties is minimal for all treatments. The alloys are most susceptible to filiform corrosion in the β′ condition. The susceptibility decreases with coarsening of the Mg₂Si particle distribution. For the post-extrusion heat and surface treated AA6063 material a clear correlation between the polarisation characteristics and the two principal filiform corrosion characteristics, i.e. the propagation rate and total area of attack after accelerated exposure, is observed. The observed correlation is attributed to a pitting corrosion mechanism with a rate depending on the (coupled) Mg₂Si precipitate size and fraction.     

Plasma immersion ion implantation induced improvements of mechanical properties, wear resistance, and adhesion of diamond-like carbon films deposited on tool steel

Nitrogen-rich layers are formed on the surface of JIS-SKH51 tool steel substrates using the plasma immersion ion implantation (PIII) technique. An unbalanced magnetron sputtering (UBMS) system is then used to coat the steel substrates with diamond-like carbon (DLC) films of various thicknesses. The adhesive strength and wear resistance of the DLC films are then examined by performing nanoscratch and nanowear tests. Finally, the microstructures of the DLC films are analyzed using TEM and Raman spectroscopy. The nanoindentation test results show that the PIII treatment yields an effective improvement in both the hardness and the Young's modulus of the SKH51 substrates. Moreover, cross-sectional observations show that the implantation depth and microstructure of the nitrogen-rich surface layer are dependent on the nitrogen/hydrogen flow ratio used in the PIII process. The nanoscratch test results show that the PIII treatment improves the adhesion of the DLC film to the steel substrate. Furthermore, the Raman spectroscopy results indicate that the use of hydrogen in the PIII process limits the increase in the I(D)/I(G) ratio by increasing the DLC film thickness. Finally, the nanowear test results show that the deposition of a DLC coating with a sufficient thickness yields a significant improvement in the wear resistance of the steel substrate.     

Corrosion of aluminium alloy A6061-T6 members embedded in alkaline materials

Owing to the corrosive conditions in coastal areas, aluminium alloy railings and similar structures are normally used on infrastructure works such as bridges and roads located in such areas because aluminium alloys are inherently corrosion resistant. However, to achieve rigid support, aluminium alloy members are often embedded in concrete. Consequently, the embedded parts undergo corrosion caused by the alkaline content of the cement used in the concrete. This research was carried out to study the corrosion behaviour on both the embedded and unembedded sides of aluminium alloy A6061-T6 members embedded in the concrete and also to investigate the ability of a combined coating of anodic oxide and organic film to inhibit corrosion. Additionally, the influence of scratch damage on the performance of this coating material was evaluated.     

Ni涂覆SiC颗粒增强Al—Fe—V—Si耐热铝基复合材料

应用新型化学涂层工艺（置换法）,成功地制备出结合紧密,光滑的Ni涂SiC粉末;分析对比了两种不同涂层工艺原理及涂层效果,分析了不同SiC增强Al-Fe-V-Si(0812)复合材料物理和力学性能,结果表明：涂覆后的SiC与基体结合牢固,涂履层（Ni)的加入降低了材料内部颗粒（SiCp)与基体（Al-Fe-V-Si)之间的 孔隙,10％SiC(Ni)(质量分数）／Al-Fe-V-Si(0812)复合材料在室温的断裂强度分别比基体和10％SiCp( 质量分数）／Al-Fe-V-Si(0812)复合材料增加了62．15％和2．82％,在400℃时分别增加了55．3％和28．6％。     

Restoring the tensile properties of PVD-TiN coated Al 7075-T6 using a post heat treatment

In this work, a post heat treatment cycle is proposed with the aim to recover the lost tensile properties of aluminium alloy 7075-T6 coated with a 3 μm thick titanium nitride (TiN) film by using a physical vapour deposition (PVD) process. First, it was found that the application of the PVD hot process with a high operating temperature of 450 °C significantly decreased the tensile properties of the coating-substrate system compared to those of Al 7075-T6. The yield and ultimate strength decreased by 78% and 54%, respectively. However, as a result of re-applying the T6 cycle (as the post heat treatment), substantial improvements of 243% and 77% were achieved in the yield and ultimate strength of the coated material, respectively. Fractography of the failed specimens indicated the TiN coating layer to be satisfactorily adhered to the substrate under tensile loading.     

采用正交试验优化Cu-Ni-Sn合金的热处理工艺

采用正交试验研究了预变形量和时效处理对新配比Cu-Ni-Sn合金(固溶态Cu-Ni-Sn合金)的力学性能的影响,并使用正交极差分析法得出最佳工艺参数。结果表明,影响Cu-Ni-Sn合金硬度的变化因素为时效温度＞预变形量＞时效时间;影响合金抗拉强度的变化因素为预变形量＞时效时间＞时效温度;影响合金断后伸长率的变化因素为时效温度>冷变形量>时效时间。由此确定最佳的工艺为时效温度360 ℃,时效时间5 h,预变形量40%。随着时效温度和预变形量的增加,合金拉伸断口形貌由大量韧窝的韧性断裂转变为河流状形貌准解理断裂,再到冰糖状沿晶脆性断裂,表明合金塑性逐渐下降。     

Study on mechanical properties and hydrogen embrittlement susceptibility of 7075 aluminium alloy

Abstract

The mechanical properties and hydrogen embrittlement susceptibility of 7075 aluminium alloy were studied by means of cathodic H permeation, hydrogen determinator, slow strain rate test (SSRT), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscope (SEM). The results showed that both before and after hydrogen charging, the strength and other properties all have double peaks for the examined alloys, and it was of excellent performance such as high strength and low hydrogen enbrittlement susceptibility under the second aging peak. Mg segregated at grain boundary during aging process, and there may exist Mg–H interaction during the hydrogen charging process, which played a significant role in hydrogen embrittlement.     

Influence of different plasma nitriding treatments on the wear and crack behavior of forging tools evaluated by Rockwell indentation and scratch tests

Forging tools are often showing short lifetimes compared to cold forming tools e.g. for sheet metal forming. This is based on the process conditions where high local surface temperatures are alternating with chilling conditions due to the spray cooling with water based cooling lubricants. The resulting thermal shock is provoking fatigue of the tool material in the near surface regions. Crack initiation and crack growth due to thermal shock exposure then causes chipping of the tool steel material in the surface regions. These are starting points for extensive wear.Hardness and wear resistance of tool surfaces at elevated temperatures can be dramatically enhanced with nitriding pretreatments. This has become state-of-the-art for hot forming tool steels in many forging applications. With inappropriate adjustments of the nitriding parameters a decrease of the ductility can occur and will reduce the crack resistance of the tool surface especially under thermal shock conditions.The hot working steel DIN-1.2367 (X38CrMoV5) is currently one of the most often used chromium-molybdenum tool steels in the field of forging. Exemplary for this material is the influence of the nitriding parameters like temperature, nitrogen supply and plasma parameters on the nitriding depth, the maximum hardness and the crack sensitivity will be discussed.Nitrided samples will be investigated with methods developed for the adhesion measurement of hard coatings. It could be shown that this is also appropriate for a qualification of the crack sensitivity of tools. Comparative application tests in the production of automotive components show the influence on the wear behavior and lifetime of forging tools in an industrial environment.