Direct laser cladding of SiC dispersed AISI 316L stainless steel

The present study concerns development of SiC dispersed (5 and 20 wt%) AISI 316L stainless steel metal-matrix composites by direct laser cladding with a high power diode laser and evaluation of its mechanical properties (microhardness and wear resistance). A defect free and homogeneous composite layer is formed under optimum processing condition. The microstructure consists of partially dissociated SiC, Cr₃C₂ and Fe₂Si in grain refined stainless steel matrix. The microhardness of the clad layer increases to a maximum of 340 VHN (for 5% SiC dispersed) and 800 VHN (for 20% SiC dispersed) as compared to 150 VHN of commercially available AISI 316L stainless steel. Direct laser clad SiC dispersed AISI 316L stainless steel has shown an improved wear resistance against diamond surface with a maximum improvement in 20% SiC dispersed AISI 316L stainless steel. The mechanism of wear was predominantly abrasive in nature.     

Erosion wear behavior of laser clad surfaces of low carbon austenitic steel

Austenitic steel surfaces are laser cladded using a 4 kW continuous wave CO₂ laser with coaxial powder feeding nozzle to investigate the improvement in slurry erosion characteristics. Colmonoy-6 and Inconel-625 are cladded on AISI 316L steel and AISI 304L steel, respectively by laser cladding. Initially, single-pass clad track is overlaid to optimize the laser processing parameters, namely scanning speed and powder feed rate to obtained a sound clad. Minimum cracks, porosity and distortion were found at scanning speed of 0.1 m/min and powder feed rate of 12 g/min. For these parameters, the dilution was 17.33% for Colmonoy-6 and 40% for Inconel-625. To clad large surface area, the optimized laser processing parameters were used to deposit the clad tracks with 60% overlap. Maximum surface hardness of 746 VHN is obtained in case of Colmonoy-6 clad on AISI 316L steel and is 352 VHN in case of Inconel-625 clad on AISI 304L steel. EDAX analysis shows higher degree of mixing of substrate material in the clad pool of Inconel-625 than Colmonoy-6. The results of slurry erosion test of Colmonoy-6 clad surface have shown improvement in erosion resistance of the order of 1.75–4.5 times of the substrate AISI 316L steel at all impact angles and the maximum wear angle has also increased which can be attributed to the increase in the surface hardness. However, Inconel-625 laser clad surface has shown little improvement in erosion resistance of the substrate AISI 304L steel at shallow impact angles with no significant improvement at normal impact condition. The SEM micrographs of worn out Colmonoy-6 clad surfaces at shallow impact angles show that the material is removed mainly by micro-cutting which increases with increase in the impact angle.     

Microstructure and Tribological Properties of a HfB<Subscript>2</Subscript>-Containing Ni-Based Composite Coating Produced on a Pure Ti Substrate by Laser Cladding

A HfB₂-containing Ni-based composite coating was fabricated on Ti substrates by laser cladding, and its microstructure and tribological properties were evaluated during sliding against an AISI-52100 steel ball at different normal loads and sliding speeds. The morphologies of the worn surfaces were analyzed by scanning electron microscopy (SEM) and three-dimensional non-contact surface mapping. The results show that wear resistance of the pure Ti substrate and NiCrBSi coating greatly increased after laser cladding of the HfB₂-containing composite coating due to the formation of hard phases in the composite coating. The pure Ti substrate sliding against the AISI-52100 counterpart ball at room temperature displayed predominantly adhesive wear, abrasive wear, and severe plastic deformation, while the HfB₂-containing composite coating showed only mild abrasive wear and adhesive wear under the same conditions.     

Wear of metals at high sliding speeds

High speed sliding wear of AISI 1020 steel, AISI 304 stainless steel and commercially pure titanium (75A) was studied using a pin-on-ring geometry. All the tests were carried out in air without any lubricant. The sliding speed was 0.5–10.0 m s^?1 and the normal force was 49.0 N (5 kgf).The friction coefficient of all the materials tested decreased with the sliding speed; this appears to be a consequence of oxide formation. The wear rate of 304 stainless steel increased monotonically with speed, whereas the wear rate of 1020 steel and titanium first decreased and then increased and again decreased, with a maximum occurring at about 5 m s^?1. The complex variation of the wear rate as a function of speed is explained in terms of the dependence of the friction coefficient, hardness and toughness of the materials on temperature. Microscope examinations of the wear track, the sub-surface of worn specimens and the wear particles indicate that the wear mode was predominantly by subsurface deformation, crack nucleation and growth processes, i.e. the delamination process, similar to the low speed sliding wear of metals. Oxidative and adhesion theories proposed in the past to explain the high speed sliding wear of metals are found to be incompatible with the experimental observations.     

Metal transfer and wear in fine grinding

The transfer and wear characteristics of two widely used abrasive materials (A1₂O₃ and SiC) are studied when grinding two difficult materials (AISI T15 tool steel and Ti-6Al-4V titanium alloy). A newly developed accelerated wear technique (cluster overcut flygrinding) is employed together with Auger electron spectroscopy, X-ray diffraction and scanning transmission electron microscopy. Experimental results suggest that when grinding steel the wear of SiC is primarily due to oxidation, while the wear of Al₂O₃ is primarily due to metal build-up, resulting in microchipping. When a titanium alloy is being ground, both types of abrasive result in a microchipping type of wear, the rate of which decreases when the wheel speed is reduced.     

MoS2/C复合涂层在不同对磨副下的冲击磨损行为研究

在基于动能控制的冲击磨损设备上,以球-平面接触的方式,探究304不锈钢基体和MoS_2/C复合涂层在不同对磨副冲击下的磨损行为,并分析摩擦界面响应及磨损机制。结果表明:随着冲击副材料的弹性模量增加,冲击接触峰值力以及能量吸收率逐渐上升,对应的磨损量及磨损率也随之提高;MoS_2/C复合涂层的接触应力、能量吸收率以及磨损均要低于304不锈钢基体;涂层的冲击磨损形式主要为材料的剥落与磨屑堆积,磨损机制为塑性变形以及摩擦氧化。     

Microstructure and sliding wear behaviour of Tribaloy T-800 coatings deposited by laser cladding

This work has focused on the obtainment of Tribaloy T-800 coatings by laser cladding on plane 18/8 stainless steel specimens (AISI 304). The appropriate selection of cladding parameters allowed defect-free coatings to be obtained with minimal dilution. In order to evaluate their microstructure, cross-sections of the coatings were examined by optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The elemental composition of the coatings was determined using an optical emission spectrometer with an excitation source (GDOES) and phase analysis was performed by X-ray diffraction (XRD). Several zones can be distinguished in the microstructure of the clad layer: a planar crystallization region at the interface with the substrate, followed by cellular and dendrite crystallization from the interface to the surface of the laser track and an overlap zone between tracks which is characterised by the coarsening of the structure and the formation of a lamellar eutectic phase. The mechanical properties were evaluated by hardness measurements and sliding wear tests (ball-on-disk and block-on-ring configurations) at room temperature and without lubrication. It was observed the great hardness (close to 850 HV_0.3) achieved for the Tribaloy 800 laser coatings, which presented a wear coefficient (k) between one and two orders of magnitude lower than the substrate. The analysis of the clad worn surfaces showed that there was a transition from an adhesive-oxidational mechanism to a more severe plastic deformation and crack formation wear process with increasing the applied load.     

Severe-to-Mild Wear Transition of Titanium Alloys as a Function of Temperature

Dry sliding wear behaviors of Ti–6Al–4V and Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloys (code-named TC4 and TC11, respectively) against AISI 52100 steel under a load of 50–250 N at 25–600 °C were systematically investigated. For two titanium alloys, a severe-to-mild wear transition occurred with an increase in temperature. The critical transition temperatures of TC4 and TC11 alloys were 400 and 300 °C, respectively. Below the critical temperature, titanium alloys showed poor wear performance. As the temperature surpassed the critical temperature, the extremely low wear rates demonstrated excellent elevated-temperature wear performance of titanium alloys in the titanium alloy/steel tribo-system. The wear transition was characterized with the appearance of continuous, hard tribo-layer containing more oxides, especially Fe₂O₃, which showed a pronounced wear-reduced role. Adhesive and abrasive wear predominated in the severe wear regime; oxidative mild wear prevailed in the mild wear regime. Adhesive wear, abrasive wear and oxidative mild wear cooperated at the critical transition temperatures.     

TEM and AES investigations of the natural surface nano‐oxide layer of an AISI 316L stainless steel microfibre

The chemical composition, nanostructure and electronic structure of nanosized oxide scales naturally formed on the surface of AISI 316L stainless steel microfibres used for strengthening of composite materials have been characterised using a combination of scanning and transmission electron microscopy with energy‐dispersive X‐ray, electron energy loss and Auger spectroscopy. The analysis reveals the presence of three sublayers within the total surface oxide scale of 5.0–6.7 nm thick: an outer oxide layer rich in a mixture of FeO.Fe₂O₃, an intermediate layer rich in Cr₂O₃ with a mixture of FeO.Fe₂O₃ and an inner oxide layer rich in nickel.     

Topographical anomaly on surfaces created by abrasive waterjet

In the present study, real topographic function and maximal depth of neglected initial zone were analytically developed to predict surface roughness on the top region of surfaces created by abrasive waterjet. An upper area of workpieces was analysed in details. Experimentally created surfaces were measured by HOMMEL TESTER T8000 and non-contact profilometer Micro Prof FRT. As an experimental material, stainless steel AISI 304, AISI 309 and aluminium with a thickness of 10?mm have been used. On the basis of analysis and interpretation of data obtained from the surface, a topography function Ra _d , which is necessary to be known for the subsequent prediction and control of abrasive waterjet cutting technology, is derived. In the framework of interpretation of measured values, relations among these parameters are systematically analysed and physico-mechanical and distributional principles governing these parameter are formulated newly. Results are very important for further estimation of analytical expression of the real topographic function for any surface created by abrasive waterjet cutting.     

Abrasive wear behaviour of sintered composite austenitic stainless steels having γ-Fe and M23C6 phases

Abstract

Using powder metallurgy, composites of austenitic stainless steel were produced along with unreinforced stainless steel mixed with titanium, cobalt and molybdenum particles. Wear resistance of the materials was measured by a two body pin on disc wear tester. SiC abrasive papers of 80 and 220 mesh sizes were used as abrasive media. Wear tests were performed under loads of 10, 20 and 30 N at room temperature. The abrasive wear measurements showed that the softer, unreinforced austenitic stainless steel exhibited higher mass loss than the composites. Furthermore, the abrasive wear resistance of the reinforced austenitic stainless steel composites increased with increasing FeTi, FeMo, or Co volume content. In addition, the wear rate against the 80 grade SiC abrasive paper increased more than against the 220 grade SiC abrasive paper.     

The Role of Reversible Martensitic Transformation in the Wear Process of TiNi Shape Memory Alloy

It has been established that the superelastic effect of TiNi alloy is related to a reversible martensitic transformation; that is, stress-induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. In the present study the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests. The effect of normal load and testing temperature on superelasticity has been investigated. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is over four times higher than TiNi. The superior wear resistance of TiNi and the effect of load and temperature on wear were discussed and related to the reversible martensitic phase transformation, as well as self-accommodation and stabilization of martensite.     

Performance of cryogenically treated M35 HSS drills in drilling of austenitic stainless steels

In this study, performance of cryogenically treated M35 high speed steel (HSS) twist drills in drilling of AISI 304 and 316 stainless steels was evaluated in terms of thrust force, surface roughness, tool wear, tool life, and chip formation. To present the differences in tool performance between untreated and treated drills, and machinability between AISI 304 SS and AISI 316 SS, a number of experiments were performed at different combinations of cutting speed, and feed rate. As the results of the conducted experiments, the treated drills showed better performance than untreated drills in terms of thrust force, surface roughness, and tool wear and tool life for both types of stainless steels. Tool lives of treated HSS drills in drilling of AISI 304 SS and AISI 316 SS improved 32% and 14%, respectively, when compared with untreated drills. Experimental results also showed that machinability of AISI 304 SS was harder than the machinability of AISI 316 SS.     

Tribology and surface mechanical properties of the oxide film formed by excimer laser surface treatment of AISI 304 stainless steel

The surface hardness and tribological properties of the surface oxide formed by excimer laser surface processing of AISI 304 stainless steel have been examined. It is found that laser processing initially anneals the stress-induced martensite on the surface of the stainless steel, resulting in a softening of the surface. After more than 100 cycles of melting and resolidification, a surface oxide film develops which is harder than the austenite of the annealed substrate and comparable in hardness to the stress-induced martensite. The thickness of the oxide film is dependent on the number of laser pulses, so that arbitrarily thick films can be produced. The dry-sliding friction of the oxide film against a steel pin is substantially lower than that of the untreated polished surface with only the native oxide film and there is substantially less damage in both the wear track and the pin. The hard surface oxide is underlain by relatively soft austenite. The tribological behavior is thus not obviously the result of the surface mechanical properties of the film-substrate combination but is ascribed to changes in the chemical interaction between the pin and the disk.     

Microstructure and wear resistance of CP titanium laser alloyed with a mixture of reactive gases

Laser processing is a promising technique for alloying and synthesis of wear resistant layers. In this work, commercially pure titanium was laser alloyed with various proportions of nitrogen and carbon monoxide in order to produce a composite surface layer. The following gas mixtures were selected: 100% N₂, 67% N₂ + 33% CO, 50% N₂ + 50% CO, 33% N₂ + 67% CO and 100% CO. The microstructure, roughness and composition of coated specimens were characterized. The presence of Ti(C,N,O) in the surface layer was assessed by X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The abrasive wear resistance of coatings was determined and related to their surface hardness. The abrasive wear resistance of the laser alloyed coating was substantially improved compared to untreated titanium and appears to be superior when composed of Ti(C,N,O) prepared from a mixture of gases.     

Damage of Stainless Steel Components by Olive Paste

Failure of equipment for processing olives interrupted oil production after only 3 weeks in service. Macroscopic and microscopic analyses were used in the present investigation to analyze damaged surfaces. Observations and data suggest that failure was induced via tribocorrosion with a predominance of mechanical damage. This damage is attributed to abrasive wear combined with corrosion of AISI 304L stainless steel in olive paste (seed particles and pulp) mixed with tap water. Microscopic observations revealed fracture and localized plastic deformation in the damaged area along with a tribologically transformed structure and work-hardened surfaces. The tribological behavior of AISI 304L was determined using a pin-on-disc tribometer, and these results were compared to damage on the olive processing equipment. The steel was sensitive to tribo-oxidation, mostly due to abrasion by seeds and steel wear particles, and somewhat due to corrosion reactions with the environment.     

Influence of the countermaterial on the dry sliding friction and wear behaviour of low temperature carburized AISI316L steel

Low temperature carburising (LTC) allows a significant hardness increase, with a consequent increase in wear resistance, without deteriorating corrosion behaviour. However, wear resistance strongly depends on contact conditions, therefore this work focuses on the dry sliding behaviour of LTC-treated AISI316L austenitic stainless steel against several countermaterials (AISI316L, LTC-treated AISI316L, hard chromium or plasma-sprayed Al₂O₃–TiO₂). LTC produced a hardened surface layer (C-supersaturated expanded austenite), which improved corrosion resistance in NaCl 3.5% and increased wear resistance, to an extent which depends on both normal load and countermaterial. The best results were obtained when at least one of the contacting bodies was LTC-treated, because this condition led to mild tribo-oxidative wear. However, LTC did not improve the behaviour in terms of friction.     

The Role of Ferric Oxide Nanoparticles in Improving Lubricity and Tribo-Electrochemical Performance During Chemical–Mechanical Polishing

The role of ferric oxide nanoparticles on the lubricating characteristics of passivating films formed on stainless steel (SS) was discussed in this study. The tribo-electrochemical behavior of mirror-like polished AISI 304 SS, used as an exemplary material, was evaluated in various electrolytes by means of a simulated chemical–mechanical polishing process in laboratory scale. It was clearly demonstrated that a suitable combination of abrasives (ferric oxide nanoparticles) and an oxidizer (nitric acid) can act as an effective lubricant that lowers the friction and wear of the AISI 304 SS surfaces. The excellent lubricating and anti-corrosion properties shown by a slurry containing a high content of ferric oxide nanoparticles at high nitric acid concentrations were attributed to the formation of a stable and robust passive film that was composed of chromium oxide and a mixture of iron oxides. The lack of ferric oxide nanoparticles in two solutions containing nitric acid of different concentrations led to pitting corrosion and abrasive wear. When low concentrations of both ferric oxide nanoparticles and nitric acid were used, wear-accelerated corrosion became the dominant mechanism that was caused by the presence of third-body wear particles in the contact zone.     

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.     

Abrasive and Adhesive Wear Behavior of Arc-Evaporated Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N Hard Coatings

During the last decade, the usage of difficult-to-machine materials such as austenitic stainless steels has increased continuously in various industrial applications. Tools such as blind hole taps, punches, or deep drawing molds are often exposed to severe wear while machining/forming these materials, mainly due to excessive adhesion and material transfer. On combination with abrasive wear due to work-hardened wear debris, tool lifetime in these applications is often limited. In this study, ball-on-disc experiments were carried out with arc-evaporated AlCrN coatings with different Al/(Al + Cr) ratios against Al₂O₃ and austenitic stainless steel balls in ambient atmosphere. Test temperatures of 25, 500, and 700°C were chosen for the hard Al₂O₃ balls simulating severe abrasive loads, whereas 25, 150, and 250°C were used for the softer stainless steel material to evaluate the adhesive wear behavior. Characterization of the wear tracks was done by scanning electron microscopy in combination with energy-dispersive X-ray analysis and optical profilometry. The best abrasive wear resistance during testing against Al₂O₃ was observed for the coating with the highest Al content. In the case of the austenitic stainless steel balls, sticking of the ball material to the coating surface was the dominating wear mechanism. The influence of test temperature, chemical composition, and surface roughness was studied in detail.