Liquid impact erosion characteristics of martensitic stainless steel laser clad with Ni-based intermetallic composites and matrix composites

NiAl-Ni₃Al intermetallic composites (IC) and intermetallic matrix composites (IMC) with TiC and WC reinforcement were laser clad to increase the liquid impact erosion resistance of AISI 420 Martensitic stainless steel. Laser process parameter optimisation and pre- and post-heat treatment of the laser clad specimens were carried out to minimise porosity and sensitivity to crack formation. The coatings were characterised by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The erosion resistance of the substrate material at a water droplet exit velocity of up to 150 m/s was improved from 116.9 to 838.7 min/mm³ for the nickel aluminide IC coating and from 855 to 1446 min/mm³ for the IMC coating with TiC and WC reinforcement. The pseudo-elasticity combined with the high work hardening ability was attributed to the excellent erosion resistance of nickel aluminide IC coatings. The IMC coatings with ceramic reinforcement extended significantly the initial resistance against liquid impact erosion. However, once damage occurred the erosion accelerated rapidly. No direct correlation could be established between the erosion resistance and the mechanical properties. The influence of hardness, elastic modulus, strain-hardening coefficient and the reversible penetration ratio on the erosion resistance was discussed.     

An Investigation into some Mechanical and Metallurgical Properties of Stainless Steel Reinforced Aluminium Alloy Powder Compacts

An experimental investigation into uniaxial tension and transverse bending of thin rectangular sheets made of stainless steel wire mesh and microcable reinforced sintered 6061 aluminium alloy powder compacts was made in order to determine some of their mechanical and metallurgical properties. Theoretical predictions based on the rule of mixtures were made for the ultimate tensile strength and for the Youngs modulus and were compared with the experimental results. Metallographic analysis involved optical and SEM photography on selected specimens and also an "EDAX" analysis on the intermetallic phase formed between the matrix and the reinforcement in order to establish its composition. In general, it was observed that the introduction of the stainless steel reinforcement resulted in extra strength of the reinforced material compared to that based on the net density of the combination.     

Delamination wear of metal injection moulded 316L stainless steel

The wear behavior of metal injection moulded (MIM) stainless steels was studied using a pin-on-disc apparatus under dry sliding conditions. Pin specimens were MIM 316L stainless steel, while disc specimens were wrought 316L stainless steel. At low sliding speeds (0.2–0.6 m/s), the wear rates gradually decreased with increasing sliding speed, but then increased at high sliding speeds (0.6–2 m/s). The adhesive-induced delamination wear dominated at low sliding speeds, while abrasive-induced delamination wear dominated at high sliding speeds. At low sliding speeds, the surface densification occurred on the worn surface of pin specimens, hence no difference was found between the wear resistances of MIM pins containing 2% and 6% porosity. In contrast, the abrasive-induced delamination wear at high sliding speeds was enhanced by porosity; therefore the wear rates of MIM pins containing 6% porosity were higher than those of MIM pins containing 2% porosity.     

增强体与粉末冶金316L不锈钢的反应性

在316L不锈钢粉中分别添加10％的TiC、WC、NbC、Al2O3、Si3N4五种增强体,研究了各种增强体与不锈钢基体的反应性及对烧结过程的影响。结果表明：TiC、WC、NbC与不锈钢基体有良好的相容性,能均匀分布到不锈钢基体中,可以有效提高其强度,添加TiC的不锈钢还表现出优越的耐腐蚀性;由于Al2O3与基体不锈钢相容性过差,不能发挥增强体的作用,使材料的强度和耐蚀性不良;添加Si3N4的不锈钢在烧结过程中Si3N4发生分解,弥散强化了基体,硅有促进烧结的作用,而氮均匀渗透到不锈钢中,有利于形成高强度的高氮钢,从而使其相对密度、硬度及耐蚀性都高于其他材料。     

激光能量密度对金属粉末直接激光烧结球化的影响

在金属粉末直接激光烧结成形时,球化效应是一个非常不利的因素。此次采用球化效应较为明显的316L不锈钢粉末进行烧结实验,分析了球化效应产生的原因,对实验中产生的规律性现象进行了解释,并着重讨论了工艺参数中的扫描速率对表面球化的影响。实验表明,当扫描速率使得激光能量密度达到合适值时,可明显降低球化效应产生的程度。     

Laser composite surfacing of AISI 304 stainless steel with titanium boride for improved wear resistance

The present study concerns development of a hard in situ boride-dispersed composite layer on the surface of AISI 304 stainless steel substrate to improve the wear resistance property. Laser processing was carried out by melting the surface of sand-blasted AISI 304 stainless steel substrate using a continuous wave CO₂ laser and simultaneous deposition of a mixture of K₂TiF₆ (potassium titanium hexafluoride) and KBF₆ (potassium hexafloroborate) (in the weight ratio of 2:1) using Ar as shrouding environment. Powder feed rate was maintained constant at 4 g/min. Irradiation results in dissociation of a pre-deposited mixture along with a part of the stainless steel substrate, intermixing and rapid solidification to form the composite layer on the surface. The micro-structure of composite layer consists of dispersion of titanium boride particles in AISI 304 stainless steel matrix. Volume fraction of particles is found to be uniform throughout the composite layer, though varied with laser parameters. The micro-hardness of the surface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel substrate with a significant improvement in wear resistance property. The mechanism of wear was found to be a combination of adhesive and abrasive in as-received stainless steel. However, it was predominantly abrasive for laser composite surfaced stainless steel.     

Erosion–corrosion of engineering steels—Can it be managed by use of chemicals?

One significant contributory factor in the degradation of both pipelines and downhole tubulars in the oil and gas industry is erosion–corrosion. An erosion–corrosion investigation was carried out with three different steels—carbon steel, martensitic stainless steel and superduplex stainless steel. The materials were chosen to represent “active” and “passive” corrosion materials and are the same materials used in completions. Tests were carried out under three different regimes spanning a range of fluid velocities to simulate the severity of the mechanical erosion effect. A commercial corrosion inhibitor was used to investigate the inhibitor ability to reduce damage due to erosion–corrosion. In each of the conditions, pure corrosion and combined erosion–corrosion were studied by electrochemical and gravimetric techniques. The experiments were conducted using a jet impingement rig capable of producing jet velocities up to 20 m/s in a CO₂-saturated environment with sand. Erosion–corrosion mechanisms were determined from microstructural studies by SEM and inhibitor adsorption tests. The paper shows that the inhibitor effectively reduced erosion–corrosion damage for carbon steel; it was only in severe erosion–corrosion conditions that inhibitor has any noticeable effect for martensitic stainless steel and there were no conditions where the inhibitor offered a benefit for the superduplex stainless steel.     

Evolution of friction-induced microstructure of SUS 304 meta-stable austenitic stainless steel and its influence on wear behavior

The microstructure evolution of the worn surface and sub-surface layer of SUS 304 austenitic stainless steel (ASS) disc against Al₂O₃ ceramic ball were studied on the basis of the tribological behaviors in the tests performed using a Cameron-Plint TE67 pin-on-disc tester. The microstructure after friction test was observed by optical and scanning electron microscope. The possible phase transformation of meta-stable austenite to martensite was detected by X-ray diffractometer. Results showed that friction-induced deformation led to finer grain at the subsurface beneath the worn surface. Furthermore, white layer was observed on some worn surface layers after higher normal loads. Transformed martensite from the austenite appeared on the worn surface under both low and high normal-loading conditions. Absence of transformed martensite was detected at the site about 25 μm below the worn surface although the grains at the site were still intensive and fine. In addition, the specific wear rate of SUS 304 stainless steel specimens was measured, and the possible reasons affecting the wear behavior were analyzed and discussed.     

The role of SAPL as a boundary lubricant in prosthetic joints

The purpose of this study was to test the potential of the body's natural lubricant, surface-active phospholipids (SAPL), to decrease friction in prosthetic joints by acting as a boundary lubricant, and to test the interaction of SAPL with Pyrolytic Carbon (PyC), a new material used in artificial heart valves and joint replacements of the upper limb. Initial testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71] slid ultra-high molecular weight polyethylene (UHMWPE) pins against highly polished stainless steel plates (surface roughness of 0.01 μm). This second series of tests was a continuation of previous research, validating the results and expanding the experiments to investigate the interaction of SAPL with PyC. In both cases, a Hounsfield test rig was used to perform the tests at ambient room conditions and at 37 °C. In both series of tests, comparative friction measurements were made using a synthetic SAPL, dipalmitoyl phosphatidylcholine (DPPC) with saline and saline only as the lubricants. When DPPC was used, the friction was reduced by 50% for the UHMWPE/SS combination, and was reduced by more than 75% for the UHMWPE/PyC combination, suggesting that DPPC acts as an effective boundary lubricant. This recent study, along with previous testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71], strongly suggests that SAPL has the ability to decrease friction in prosthetic joints by acting as a boundary lubricant, and that SAPL interacts favourably with PyC.     

Microstructural analysis of a FeAl/quasicrystal-based composite prepared using a focused ion beam miller

A composite consisting of a brittle multiphase matrix containing both an Al-based quasicrystalline phase (ψ) and an ordered body centred cubic phase (β) and a relatively ductile ordered body centred cubic intermetallic FeAl phase has been developed as an abrasive wear-resistant coating material. It is applied as a 500 μm thick layer onto stainless steel substrates through plasma spray processing. The microstructure of such materials can be readily examined by optical and scanning electron microscopy, but the inherent difficulty of preparing transmission electron microscope (TEM) samples has inhibited higher resolution studies. However, the relatively recent development of the focused ion beam (FIB) miller as a tool in materials science provides a method ideal for the preparation of TEM specimens of these materials. In this study a coating consisting of a mixture of an Al–Cu–Fe based quasicrystal and FeAl+Cr was deposited on to a 304 stainless steel substrate. TEM specimens were prepared using a FIB and subjected to detailed microstructural characterization. The structure consisted of elongated bands of a FeAl phase about 100 nm in width and several micrometres in length, which enclosed more equiaxed regions about 1 μm in diameter that consisted of fine mixtures of quasicrystal and two Al-Fe-Cu phases isostructurally related to FeAl.     

Dry sliding wear behaviour of polyamide 66 and polycarbonate composites

A study has been made of the reciprocating dry sliding wear behaviour of polyamide 66 and polycarbonate containing glass fibres, ultra high molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE/2% Si oil). Studies have been conducted at sliding loads of 2 kg and 10 kg at an average velocity of 0.33 m s⁻¹ against a hardened stainless steel counterface with a surface roughness of 0.3 μm.It has been shown that additions of 10–15% of filler/reinforcement lead to greatly improved sliding wear behaviour. PTFE/2% Si oil filled polyamide 66 has been shown to have the best overall wear performance whilst the high glass filled variants of polyamide 66 and polycarbonate have the best combination of wear resistance and mechanical strength. These findings are discussed with reference to composite constitution and properties, thermal effects and counterface interactions. Explanations are advanced to account for the differences in behaviour inter alia the composite materials.     

Potential of kenaf fibres as reinforcement for tribological applications

This paper presents an attempt to use kenaf fibres as reinforcement for tribo-composite based on epoxy for bearing applications. Kenaf fibres reinforced epoxy (KFRE) composite was fabricated using a closed mould technique associated with vacuum system. Sliding wear and frictional behaviour of the composite were studied against polished stainless steel counterface using Block-On-Disc (BOD) machine at different applied loads (30–100 N), sliding distances (0–5 km) and sliding velocities (1.1–3.9 m/s). The effect of the fibre orientations, with respect to the sliding direction, was considered; these orientations are parallel (P-O), anti-parallel (AP-O) and normal (N-O). The morphology of the worn surfaces of the composite was studied using a scanning electron microscope (SEM). The result revealed that the presence of kenaf fibres in the composite enhanced the wear and frictional performance of the epoxy. Applied load and sliding velocity have less effect on the specific wear rate of the composite in all the three orientations. The composite exhibited better wear performance in N-O compared to P-O and AP-O.     

The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

Erosion–corrosion and corrosion properties of DLC coated low temperature gas-nitrided austenitic stainless steel

Low temperature nitriding of stainless steel leads to the formation of a surface zone of so-called expanded austenite, i.e. by dissolution of large amounts of nitrogen in solid solution. In the present work the possibility of using nitrogen expanded austenite “layers” obtained by gaseous nitriding of AISI 316 as substrate for DLC coatings are investigated. Corrosion and erosion–corrosion measurements were carried out on low temperature nitrided stainless steel AISI 316 and on low temperature nitrided stainless steel AISI 316 with a top layer of DLC. The combination of DLC and low temperature nitriding dramatically reduces the amount of erosion–corrosion of stainless steel under impingement of particles in a corrosive medium.     

Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods

The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel.The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy.The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5–10 μm in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.     

A study of the wear behavior of polymer–matrix composites containing discontinuous nanocrystalline alloy reinforcements

The tribological behavior of bakelite resin–matrix composites reinforced with nanocrystalline Al 6061 T6 particles produced by machining (grain size 70–500 nm) has been studied using block-on-ring and pin-on-disk tests. The polymer–matrix composite reinforced with nanostructured Al 6061 particles aged for 10 h [Al 6061 (3) 10 h] shows a wear reduction of around 60% with respect to the conventional microstructured reinforcement. Also it shows the lowest wear rates when compared with the nanostructured reinforcements aged for 5 h or 1 h, respectively. Friction coefficients and wear rates increased with increasing sliding speed and normal load. Under 10 N and 0.10 m s⁻¹, Al 6061 (3) 10 h showed an initial friction and contact temperature increase and a very severe wear with material transfer to the steel ball surface. Increasing the steel–composite contact temperature to 100 °C (1 N; 0.05 m s⁻¹) produced a one order of magnitude decrease both in friction and wear. Wear mechanisms for the polymer matrix and the aluminum reinforcement are discussed on the basis of SEM and EDS observations.     

Friction and wear scar analysis of carbon nanofiber-reinforced polymeric composite coatings on alumina/aluminum composite

Alumina/aluminum based composites with excellent physical and mechanical properties offer great potential for lightweight, wear resistant, and high temperature applications. The objective of the present research was to investigate a suitable coating material to provide a low coefficient of friction (COF) during sliding contact. The friction behavior of carbon nanofiber-reinforced aerospace polymer coatings prepared by the spin coating technique were investigated. Polymethylmethacrylate (PMMA), bis A polycarbonate, and two biphenyl endcapped poly(arylene ether phosphine oxide) compositions, namely BPETPP-E and 6FETPP-E, were used as the matrices. Pin-on-disc experiments were performed between 440C stainless steel balls and disc samples of coated alumina/aluminum interpenetrating phase composites at 0.2 m/s sliding velocity, in air, at room temperature under 0.25 and 0.74 N normal load. In all cases, formation of a lubricious carbon layer and its transfer to the steel counterface was observed to result in lower COF (∼0.2–0.3). Higher levels of fiber content (40 and 60 wt.% fibers) contributed to a faster formation of this layer. Wear scar analysis showed the dual roles of the carbon nanofibers, serving as solid lubricants and as reinforcement in the coatings. The amount of debris generated and the coverage of the lubricious carbon-rich film on the scar surface was dependent on the matrix material used. Adherent and uniform coverage of a lubricious carbon-rich film at the wear contact with the least amount of debris fragments was obtained only for composite coatings using BPETPP-E and 6FETPP-E matrices.     

Reduction of the sliding friction of metals by the application of longitudinal or transverse ultrasonic vibration

The influence on sliding friction of ultrasonic vibration both parallel and perpendicular to the sliding direction has been studied for samples of aluminium alloy, copper, brass and stainless steel sliding against tool steel. Experiments were performed at a mean sliding speed of 50 mm s⁻¹, and at mean contact pressures up to 0.7 MPa, with vibration amplitudes up to 10 μm at 20 kHz. Significant reduction in sliding friction was observed (up to >80%) and good agreement was found between the measured values and the predictions of two simple models for the effects of longitudinal and transverse vibrations. Longitudinal vibration produces greater reduction in friction than transverse vibration at the same amplitude and frequency. At high vibration amplitudes, the reduction in friction was less than that predicted by the models, because significant metallic transfer occurred from the softer metals to the tool steel counter surface.     

Erosion–corrosion assessment of materials for use in the resources industry

The erosion–corrosion properties of a range of ferrous-based materials that are currently being used or have potential for use in the resources industry have been assessed using a slurry pot erosion–corrosion (SPEC) test rig that has the capability of establishing the separate components of erosion, corrosion and synergy.Testing was performed, at 30 °C, in an aqueous slurry containing 35 wt% AFS 50–70 silica sand and a 3.5 wt% NaCl solution. Erosive action was supplied through high-speed rotation of a rubber-lined impeller.Erosion–corrosion performance of materials evaluated was related to composition/microstructure and hardness. Test data correlated with available service experience.The results showed that the cast Cr white irons with (i) a structure that was essentially a duplex stainless steel containing a distribution of hard carbides and (ii) a near eutectic Cr white iron exhibited the highest erosion–corrosion resistance of the materials tested. The evaluation of the Cr white irons also highlighted the influence of Cr and C levels on the E–C properties of these materials.E–C assessment of selected carbon steels confirmed that the erosion-only rates and synergistic levels showed a general decline with increasing carbon content and hardness. As expected, a low C steel pipe product displayed very mediocre erosion–corrosion behaviour as a consequence of its very low intrinsic corrosion resistance and inferior wear properties. This reflected service experience, however, such products are still being used, due to the comparatively low initial cost.A TiC particle-reinforced AISI 316 stainless steel exhibited an almost 45% improvement in the E–C resistance, when compared with an AISI 316L stainless steel.     

Electro-chemical micro drilling using ultra short pulses

Electro-chemical machining (ECM) has been rarely applied in micro machining because the electric field is not localized. In this work, ultra short pulses with tens of nanosecond duration are used to localize dissolution area. The effects of voltage, pulse duration, and pulse frequency on the localization distance were studied. High quality micro hole with 8 μm diameter was drilled on 304 stainless steel foil with 20 μm thickness. Localization distance can be manipulated by controlling the voltage and pulse duration, and various hole shapes were produced including stepped holes and taper free holes.