Abrasive resistance of arc sprayed carbonitride alloying self-shielded coatings

Wear-resistant coatings were prepared on the surface of the Q235 low-carbon steel plate by HVAS with the carbonitride alloying self-shielded flux-cored wire. Detection and analysis on the microstructure and properties of the coatings were carried out by using scanning electron microscope, microhardness tester and wear tester. The forming, the wear resistance and its mechanism of the coatings were studied. The results show that the coatings have good forming, homogeneous microstructure and compact structure. The coatings have good hardness, the average microhardness value reaches 520 HV_0.1, and the highest value is up to about 560 HV_0.1. As a result, the coatings have good abrasive wear performance and adhesion strength.     

Preparation and characterization of SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Na<Subscript>2</Subscript>O glass coated cBN abrasive particles via sol–gel route

SiO₂–Al₂O₃–Na₂O glass coated cubic boron nitride (cBN) abrasive particles were prepared by sol–gel technique. The results indicated that SiO₂–Al₂O₃–Na₂O glass was excellent material for oxidation protection of cBN abrasive grains because coefficient of thermal expansion of this glass closely matched that of cBN materials. The single particle compressive strength and impact toughness of this glass coated cBN abrasive particles were significantly increased. For the application of glass coated cBN abrasives to vitrified grinding wheels, it was evident that the glass coating provided high bonding strength between cBN abrasive grains and vitrified bond system.     

Accelerated wear testing of polyurethane hydraulic seal

The wear characteristics of a polyurethane (PU) hydraulic seal were investigated using a hydraulic seal tester and a pin-on-plate reciprocating tribo-tester, and the results were compared to field data with the aim of developing an accelerated wear test method for hydraulic seals. Tests using a hydraulic seal tester and a pin-on-plate reciprocating tribo-tester were found to reproduce abrasive wear of PU from the field. However, a significant compression set was observed from the test using the hydraulic seal tester. Motivated by the occurrence of abrasive wear from the field, the discolored lubricant and the lubricant with alumina particles were further used for testing using the pin-on-plate reciprocating tribo-tester. The height decrease data of the sealing surface showed that the wear was accelerated by factors of 2.1–3.4 using these degraded lubricants. The outcomes of this work are expected to aid in the design of reliable accelerated life testing for hydraulic seals.     

Investigation of displacement fields in an abrasive waterjet drilling process: Part 1. Experimental measurements

The transient state of displacement fields in the machining zone of a target material during abrasive waterjet impinging and drilling was investigated. A moiré interferometry experimental setup for recording displacement fields and a dynamometer for measuring the reaction force were developed. Whole fields of surface displacement fields and the reaction force of the ceramic and polycarbonate target materials were successfully recorded when the specimen was being pierced by high-pressure abrasive waterjet (AWJ). This paper demonstrates that bothu andv displacement fields of a workpiece during AWJ drilling can be recorded in real time and simultaneously by the moiré interferometry experimentation. The measured surface displacement distributions and the machining forces will be used to drive a finite element model in the second part of this investigation, in which the authors study the stress and strain state for the target material associated with the jet-materials interaction during the jet penetration process.     

Monitoring acoustic emission (AE) energy of abrasive particle impacts in a slurry flow loop using a statistical distribution model

Slurry erosion has been recognized as a serious problem in many industrial applications. In slurry flows, the estimation of the amount of incident kinetic energy that transmits from particles suspended in the fluid to the containment structures is a key aspect in evaluating its abrasive potential. This work represents a systematic investigation of particle impact energy measurement using acoustic emission (AE), as indicated by a sensor mounted on the outer surface of a sharp bend, in an arrangement that had been pre-calibrated using controlled single and multiple impacts. Particle size, free stream velocity, and nominal particle concentration were varied, and the amount of energy dissipated in the carbon steel bend was assessed using a slurry impingement flow loop test rig. Silica sand particles of mean particle size 225–650 μm were used for impingement on the bend with particle nominal concentrations between 1 and 5% while the free stream velocity was changed between 4.2 and 14 ms⁻¹.     

Novel cavitation fluid jet polishing process based on negative pressure effects

Traditional abrasive fluid jet polishing (FJP) is limited by its high-pressure equipment, unstable material removal rate, and applicability to ultra-smooth surfaces because of the evident air turbulence, fluid expansion, and a large polishing spot in high-pressure FJP. This paper presents a novel cavitation fluid jet polishing (CFJP) method and process based on FJP technology. It can implement high-efficiency polishing on small-scale surfaces in a low-pressure environment. CFJP uses the purposely designed polishing equipment with a sealed chamber, which can generate a cavitation effect in negative pressure environment. Moreover, the collapse of cavitation bubbles can spray out a high-energy microjet and shock wave to enhance the material removal. Its feasibility is verified through researching the flow behavior and the cavitation results of the negative pressure cavitation machining of pure water in reversing suction flow. The mechanism is analyzed through a computational fluid dynamics simulation. Thus, its cavitation and surface removal mechanisms in the vertical CFJP and inclined CFJP are studied. A series of polishing experiments on different materials and polishing parameters are conducted to validate its polishing performance compared with FJP. The maximum removal depth increases, and surface roughness gradually decreases with increasing negative outlet pressures. The surface becomes smooth with the increase of polishing time. The experimental results confirm that the CFJP process can realize a high material removal rate and smooth surface with low energy consumption in the low-pressure environment, together with compatible surface roughness to FJP.     

Application of abrasive stripping voltammetry in corrosion science. I. determination of the corrosion potentials of metals

The application of abrasive stripping voltammetry for the determination of the corrosion potential of metal powders is described. Micro amounts of a metal are fixed on a paraffin-impregnated graphite electrode immersed in suitable electrolyte solutions and polarization curves are recorded. The value of the corrosion potential is determined by Tafel analysis. The precision of the method is ±0.5% (mean rel. dev.) of the final potential value. Received: 24 March 1998 / Accepted: 27 August 1998     

Voltammetry as an Alternative Tool for Trace Metal Detection in Peloid Marine Sediments

Here was demonstrated for the first time a possible application of abrasive stripping voltammetry in the direct measurement of trace metals in anoxic, sulfidic marine sediments (peloid mud) from a small and shallow (0.2–1 m) marine lagoon in Central Dalmatia, Croatia. Trace amounts of sample compounds are transferred to the graphite electrode surface and electrochemical reduction or oxidation processes are followed by the cyclic voltammetry in seawater or 0.55 M NaCl as electrolyte. After a preelectrolysis at potentials ranging from ?1.0 to ?1.5 V (vs. SCE) a well‐defined anodic stripping peak corresponding to the oxidation of metal deposits generated at deposition potentials is obtained around ?0.74 V (vs. SCE). The same samples were studied by anodic stripping voltammetry at the Hg electrode and inductively coupled plasma‐mass spectrometer (ICP‐MS). ICP‐MS showed higher concentrations of trace metals such as Al, Fe, Mo, Mn. A relatively high concentration of reduced sulfur species (RSS) (10^?3 M) is determined electrochemically in porewater of the peloid mud, indicating that the magnitude of metal enrichment in the sediments is probably controlled by precipitation with sulfide.     

Effect of carbonitride precipitates on the abrasive wear behaviour of hardfacing alloy

Hardfacing alloy of martensitic stainless steel expect higher abradability to be achieved through the addition of nitrogen being provided by the fine scale precipitation of complex carbonitride particles. Niobium and titanium as the most effective carbonitride alloying elements were added in the Fe–Cr13–Mn–N hardfacing alloy to get carbonitride precipitates. Carbonitride was systematically studied by optical microscopy, scanning electronic microscopy and energy spectrum analysis. Abrasive wear resistance of hardfacing alloy in as-welded and heat-treated conditions was tested by using the belt abrasion test apparatus where the samples slide against the abrasive belt. It is found that carbonitride particles in the hardfacing alloy are complex of Cr, Ti and Nb distributing on the grain boundary or matrix of the hardfacing alloy with different number and size in as-welded and heat-treated conditions. A large number of carbonitrides can be precipitated with very fine size (nanoscale) after heat treatment. As a result, the homogeneous distribution of very fine carbonitride particles can significantly improve the grain-abrasion wear-resisting property of the hardfacing alloy, and the mass loss is plastic deformation with minimum depth of grooving by abrasive particles and fine delamination.     

松孔镀铬层的高效超声珩磨

作者使用自行研制的立式超声珩磨装置对钢质薄壁气缸套松孔镀铬层进行了超声珩磨试验。试验结果使用人造金刚石和ＣＢＮ油石时，与普通珩磨相比，超声珩磨镀铬层可提高珩磨效率１４－５９倍，表面粗度Ｒａ可达０．２－１．２７μｍ，加工精度可达ＩＴ６－ＩＴ７。