Supersonic Fine Particles Bombarding Research Articles

Effect of surface nano-crystallization induced by supersonic fine particles bombarding on microstructure and mechanical properties of 300M steel

Supersonic fine particles bombarding (SFPB) technology opens a new territory for engineering materials towards improved performances. Owing to its merits and emerging applications, 300M steel (tensile strength ≥1800 MPa) was treated with SFPB to create surface gradient nanostructures. The time dependent SFPB process was implemented on various 300M steel surface to investigate the microstructural evolution and mechanical property. 300M steel surface grains were sufficiently refined down to nanometer scale under high energy SFPB. In the subsurface layer, acicular martensite was found to be bent and broken, resulting in the high-density dislocation. At the early stage of SFPB, the impact affected area of 300M steel surface was deepened with increasing SFPB time, and the grains were constantly refined, which further lead to higher strength and improved hardness. However, after longer treatments of more than 90 s, bombardment energy accumulated at 300M steel surface resulted in grain growths and deteriorations of hardness. In particular, the newly formed microcracks substantially reduced the tensile strength. After SFPB treatment, the dimple size of the 300M steel surface fracture decreased significantly, and a large area of cleavage plane appeared, showing typical characteristics of ductile-brittle mixed fracture.

Influence of surface nanocrystallization pretreatment on high-temperature vacuum carburizing behavior

Abstract The supersonic fine particles bombarding (SFPB) pretreatment is adopted to assist vacuum carburizing for refining the microstructure and improving the mechanical properties of carburized layer. The microstructures, micrhardness and tribology properties of SFPB carburized sample and vacuum carburized sample were studied. The results showed that SFPB pretreatment could form random oriented, ultrafine-grained microstructure and high density dislocations in AISI 9310 steel, leading to the increase of case depth of carburized layer, the refinement of grain size and the promotion of the formation of twin martensite and carbides in carburized layer. Besides, the surface microhardness, maximum residual compressive stress and wear rate of carburized layer were enhanced by SFPB pretreatment, which was attributed to the formation of twin martensite, grain refinement, dispersion strengthening of carbides and the increase of high misorientation angle grain boundary.

Effect of surface nanocrystallisation on the microstructure and wear resistance of vacuum carburised alloy

ABSTRACTIn this work, a nanocrystallisation surface layer with an average grain size of 29 nm was fabricated on the 12Cr2Ni4A steel by the supersonic fine particles bombarding (SFPB). The vacuum carburising process was carried out on the original and the SFPB pre-treatment samples. X-ray diffraction, scanning electron microscopy and hardness tester were employed to study the phase constituents, grain size, hardness and residual stress of the two carburised samples. Experimental results showed that compared to the coarse-grain carburised layer (without SFPB), the carburised layer with SFPB pre-treatment has smaller martensite and carbide, and its thickness, hardness, compressive residual stress and wear resistance have been significantly improved. The dominant wear mechanisms of the two carburised samples were both abrasive wear and fatigue wear.

Tribological Properties of Surface-Textured and Plasma-Nitrided Pure Titanium Under Oil Lubrication Condition

Plasma nitriding was conducted as post-treatment for surface texture on pure titanium to obtain a continuous nitriding layer. Supersonic fine particles bombarding (SFPB) was carried out to prepare surface texture. The surface morphologies and chemical composition were analyzed using scanning electron microscope and energy disperse spectroscopy. The microstructures of modified layers were characterized by transmission electron microscope. The tribological properties of surface-textured and duplex-treated pure titanium under oil lubrication condition were systematically investigated in the ball-on-plate reciprocating mode. The effects of applied load and sliding velocity on the tribological behavior were analyzed. The results show that after duplex treatments, the grains size in modified layer becomes slightly larger, and hardness is obviously improved. Wear resistance of duplex-treated pure titanium is significantly improved referenced to untreated and surface-textured pure titanium, which is 3.22 times as much as untreated pure titanium and 2.15 times of that for surface-textured pure titanium, respectively.

Electrochemical corrosion property of nanostructure layer of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy

Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy was nanocrystallized with supersonic fine particles bombarding (SFPB). The microstructure features of nanocrystalline layer were determined by XRD, TEM, and microhardness tester. The electrochemical corrosion properties of the surface of original sample and the nanocrystallized sample surface were tested by CHI660 tester. That random crystallographic oriented particles (average grain size of 16 nm) were observed in the top surface layer of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy, which could be attributed to the surface nanocrystallization. The electrochemical corrosion results show that the impedance of the sample nanolayer is reduced after SFPB with 30 min, and the corrosion resistance is lower than the original sample. The residual internal stress from the process of SFPB is one of the main factors to decrease the nanolayer corrosion resistance of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy. However, the corrosion resistance is significantly recovered after stress relief annealing with 250–350 °C.

Influence of isothermal aging conditions on APS TBC's interfacial fracture toughness

Interfacial toughness is an important factor to address thermal barrier coating's (TBC) durability. In this paper, a promising method, based on interfacial indentation, is used to analyze apparent interfacial toughness of TBC deposited by Atmospheric Plasma Spray (APS). The specimens made by APS were treated using different oxidation holding times and temperatures, namely 1050°C-100h, 1100°C-100h, 1050°C-300h and 1100°C-300h, respectively. The morphology of the interface between the TBC and the underlying bond coat was analyzed by Scanning Electron Microscopy (SEM). Results have shown that the fracture toughness of the interface between the bond coat and the top coat decreased as the oxidation conditions become more severe that is the temperature and/or to a lesser extent the exposure time is increased. Simultaneously, the thickness of the thermally grown oxide (TGO) generated on top of the aluminum reservoir bond coat increases as well. The TGO is a “double layer” oxide successively composed of a first scale of Al2O3 close to the bond coat and a second scale of CoCrNiO close to top coat. In addition, it was also found that the possible thermally activated spallation of APS TBC's system occurs in the zone of the TGO layer, especially within the CoCrNiO oxide scale. Consequently damage of APS systems is shown to initiate at the interface through complex mechanism of delamination in relation with both the toughness and the microstructure of the interface. In order to inhibit the growth of the detrimental CoCrNiO oxide and in turn favors the development of a dense and stable alumina scale, a Supersonic Fine Particles Bombarding (SFPB) method was used to optimize the quality of APS coating.

Research on Mechanism of Surface Nanocrystalline Layer in 2219 Al Alloy Induced by Supersonic Fine Particles Bombarding

A nanostructured surface layer is formed on 2219 Al alloy plate by means of supersonic fine particles bombarding (SFPB). The surface microstructure formation mechanism of morphology change is systematically characterized by using scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average grain size of 30nanostructured layer is about 30 nm when the surface of sample is induced by severe plastic deformation. Based on the experimental observations, nanoscale dislocation cells exist in strain layer about 200 from the surface, and we put forward a new formation mechanism of Al alloy surface nanocrystalline layer through theoretical analysis. The original grain is segmented fast into nanoscale dislocation cell or lamellar cell. As the Burgers vector of cell walls continue to accumulate, grain orientation difference constantly increases to form the nanoscale subboundary. Eventually, equiaxed nanocrystallites with random crystallographic orientations are formed by grain rotating or grain boundary sliding.

Evolution mechanism of surface nano-crystallization of tungsten-copper alloys

A nanostructure surface layer was fabricated on CuW70 alloy by supersonic fine particles bombarding (SFPB) technology. The microstructure features of the surface layer were characterized by using XRD, SEM, TEM observations. The results show that severe plastic deformation was produced on the surface of SFPB-treated CuW70 alloy, a part of W particles were fragmented and become smaller on the surface, while the Cu particles only exhibit deformation. The thickness of nanostructure surface layer increased depending upon the treatment duration, the well technology was shot peening 60min, in this case, the thickness up to 21µm, the grain refinement process of CuW70 alloy involved internal defects proliferation, particles deformation and break up, grain refining of W, and strong plastic deformation of Cu bonding phase. Finally, the random orientation of nano-crystal was formed on the surface.

Microstructure and tribological performance of a dimpled gradient nanoscale TiN layer

The dimpled gradient nanoscale TiN (nano-TiN) layer was prepared on the pure Ti surface by the combined process of supersonic fine particles bombarding (SFPB) and glow-discharge plasma nitriding. A large numbers of dimples (30–40µm in diameter) homogenously distribute on the prepared nano-TiN layer surface and are beneficial to the reservation of oil and wear debris during friction process. The nano-TiN layer is about 25µm in thickness with a three-layered nanoscale structure and the grain size decreases sequentially from the outer layer to the inner one. The nano-TiN layer with higher mechanical properties displays enhanced friction and wear reducing effects compared to the SFPB-dimpled Ti surface.

Electrochemical corrosion properties of the surface layer produced by supersonic fine-particles bombarding on low-carbon steel

A grain refined surface layer thicker than 15μm was fabricated on a low-carbon steel by supersonic fine-particles bombarding (SFPB). The microstructure and electrochemical corrosion properties of the original and the SFPB treated (SFPB-ed) low-carbon steel were characterized by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and corrosion tests. The results showed that the microstructure of the top surface layer was refined to fine grains with the grain size about 3μm by SFPB. Dislocation tangles and dense dislocation cells about 500nm in width were formed in the refined grains. Large amounts of micro-cracks were introduced into the surface layer of the SFPB-ed sample, which led to the increase of its surface roughness. The SFPB treatment accelerated the corrosion of the low-carbon steel in a neutral 3.5wt.% NaCl solution. The surface layer of the SFPB-ed low-carbon steel was dissolved after a certain time of corrosion, which led to the decrease of its corrosion rate. In a saturated Ca(OH)2 solution with and without Cl−, the micro-cracks in the surface layer of the SFPB-ed sample did not degrade its passivity properties and pitting resistance, which was due to the superior re-passivation properties of the abundant crystalline defects in its surface layer, such as grain boundaries and dislocations.

Nanocrystalline Surface Layer on AISI 52100 Steel Induced by Supersonic Fine Particles Bombarding

Surface treatment of AISI 52100 steel by supersonic fine particles bombarding (SFPB) was studied in this article. The surface topography, morphology of the surface layer, and microhardness distribution of the surface layer have been investigated using a surface profiler system, a scanning electron microscopy (SEM), and a microvickers hardness tester. The microstructure, phase composition, and residual stress distribution of the surface layer in AISI 52100 steel after the SFBP treatment have been characterized by means of x-ray diffraction, SEM, and transmission electron microscopy. The results showed that a nanocrystalline surface (NS) layer was formed on the top surface of the SFBP-treated AISI 52100 steel samples. The NS layer is about 2 μm in thickness with a surface roughness of Ra = 1.2 μm, Ry = 6.7 μm, Rz = 6.0 μm. Phase transitions occurred in the surface of the SFBP-treated samples. Residual compressive stress is obtained at the surface of the SFBP-treated samples. The maximum value of compressive stress appears at the outermost of the surface, and the affection region of the whole surface is about 60 μm in thickness. A hardened surface layer has been fabricated in the AISI 52100 steel. The thickness of the hardened surface layer is about 70 μm. The maximum value of hardness occurs at the depth of 20 μm from the outermost surface.

Effects of supersonic fine particles bombarding on thermal barrier coatings after isothermal oxidation

This work was attempted to modify the current technology for thermal barrier coatings (TBCs) by adding an additional step of surface modification, namely, supersonic fine particles bombarding (SFPB) process, on bond coat before applying the topcoat. After isothermal oxidation at 1000 °C for different time, the surface state of the bond coat and its phase transformation were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and Cr3+ luminescence spectroscopy. The dislocation density significantly increases after SFPB process, which can generate a large number of diffusion channels in the area of the surface of the bond coat. At the initial stage of isothermal oxidation, the diffusion velocity of Al in the bond coat significantly increases, leading to the formation of a layer of stable α-Al2O3 phase. A great number of Cr3+ positive ions can diffuse via diffusion channels during the transient state of isothermal oxidation, which can lead to the presence of (Al0.9Cr0.1)2O3 phase and accelerate the γ→θ→α phase transformation. Cr3+ luminescence spectroscopy measurement shows that the residual stress increases at the initial stage of isothermal oxidation and then decreases. The residual stress after isothermal oxidation for 310 h reduces to 0.63 GPa compared with 0.93 GPa after isothermal oxidation for 26 h. In order to prolong the lifespan of TBCs, a layer of continuous, dense and pure α-Al2O3 with high oxidation resistance at the interface between topcoat and bond coat can be obtained due to additional SFPB process.

Effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti stainless steel

Surface nanocrystallization of 1Cr18Ni9Ti austenite stainless steel was conducted by the supersonic fine particles bombarding (SFPB) technique. The friction coefficients and wear losses in air and vacuum were tested to analyse the effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti steel. The results show that the microstructure of the surface layer was refined into nano-grains successfully by SFPB treatment; furthermore, strain-induced martensitic transformation occurred during the treatment. The tribological properties of SFPB treated samples enhanced greatly, The dominant wear mechanism of the original 1Cr18Ni9Ti stainless steel is abrasive wear and adhesive wear, while it transfers to the combined action of fatigue wear, abrasive wear and adhesive wear after surface nanocrystallization by SFPB.

Effect of Surface Nanocrystallization Pretreatment on the Tribological Properties of Sulfide Layers of 1Cr18Ni9Ti Stainless Steel

A nanocrystalline layer is prepared on the 1Cr18Ni9Ti stainless steel by using supersonic fine particles bombarding(SFPB) surface nanocrystallization technique.And the grain size of the randomly oriented equiaxial nanograins is about 30 nm.Then,some of the original and SFPB treated(SFPBed) 1Cr18Ni9Ti samples are sulfurized by low-temperature ion sulfurization process and obtained sulfide layers,respectively.The tribological properties of the 1Cr18Ni9Ti before and after SFPB treatment and the corresponding two kinds of sulfide layers are investigated using a УТИ-1000 type ball-on-disk tribometer under dry friction.The results show that the tribological properties of 1Cr18Ni9Ti steel and the effectiveness of sulfurization are enhanced remarkably by surface nanocrystallization treatment.The friction coefficient of the SFPBed 1Cr18Ni9Ti steel with nanocrystalline surface layer descend from 0.65 to 0.45,while the thickness of the sulfide layer on the SFPB pretreated sample increased from 1 μm to 3.5 μm.These modifications can be mainly attributed to the high hardness,strength and chemistry activity of the nanocrystalline surface layer.The predominant wear mechanisms of the original 1Cr18Ni9Ti steel are abrasive wear and adhesive wear,and they transform to fatigue wear after surface nanocrystallization treatment.

Effect of Supersonic Fine Particles Bombarding on the Service Life of Thermal Barrier Coating

Thermally Grown Oxide(TGO) is a dominating component in controlling the effectiveness of thermal barrier coating.During the growth of TGO,whether we could homogeneously distribute Al atom on the TGO and the intermediate metal layer will be the key factor in forming TGO with continuous,uniform and single-ingredient(Al2O3).In this experiment,we bombarded particles on to the metallic bound layer.We studied the influence of supersonic particle bombardment on the diffusion of Al.We hope to control the growth of TGO by monitoring the diffusion of Al.Thermal barrier coating(TBC),which consists of a NiCoCrAlY bond coat and a ZrO2-8Y2O3(wt.%) topcoat(TC),is fabricated on the nickel-base superalloy by air plasma spray(APS).NiCoCrAlY bond coat is treated by supersonic fine particles bombarding(SFPB).The morphology,oxidation behavior of TBC and phase are characterized by scanning electron microscope(SEM) equipped with an energy dispersive spectromrter(EDS) and X-ray diffractometer(XRD).The influence of supersonic fine particles bombarding technique on the service life of thermal barrier coating is studied.The results show that SFPB technique improves the flaw of excessive surface undulation in the as-sprayed bond coat.A continuous,uniform and single-ingredient(Al2O3) TGO can quickly form in the SFPB TBC during high temperature oxidation process.The thickening of TGO is relatively slow.These will effectively suppress the formation of other non-protective oxides.Therefore,SFPB technique reduces the growth stress level generated by the continuous growth of TGO,and also avoids the stress concentration induced by formation of the large particle spinal oxide.Thermal barrier coating still remains well after 350 thermal cycles.The service life of TBC is improved.The proposed research provides theoretical basis and technical references to further improve and enhance the SFPB technique.

Microstructure and vacuum tribological properties of 1Cr18Ni9Ti steel with combined surface treatments

A sulfide film was fabricated on the nanocrystalline layer of 1Cr18Ni9Ti stainless steel by a two-step method of supersonic fine particles bombarding (SFPB) and low temperature ion sulfurization treatments. The microstructure and mechanical properties of the nanocrystallized surface and the sulfide film were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy (equipped with EDS), augur energy spectroscopy, X-ray photoelectron spectroscope, and nano-indenter. The tribological behaviour of the treated (after SFPB and sulfurizing treatments) 1Cr18Ni9Ti steel in vacuum was investigated on a ball-on-disk tribometer. The results showed that, randomly oriented equiaxial nanograins with the mean grain size less than 30nm were formed in the top surface layer of the SFPB treated sample, and a compact and uniform sulfide film mainly composed of FeS was obtained after the succedent sulfurizing treatment. Compared to the original 1Cr18Ni9Ti steel, the treated surface revealed lower friction coefficient and better wear resistance in vacuum, and the variation of tribological properties with atmospheric pressure of the treated samples was not significant. The dominant wear mechanisms of the treated 1Cr18Ni9Ti in vacuum were abrasive wear and fatigue wear.

Effects of surface nanocrystallization pretreatment on low-temperature ion sulfurization behavior of 1Cr18Ni9Ti stainless steel

A nanocrystalline surface layer of 10 μm thickness was fabricated on 1Cr18Ni9Ti stainless steel by means of supersonic fine particles bombarding (SFPB). The followed low-temperature ion sulfurizing was carried out on the original and the SFPBed (SFPB treated) surface, respectively, forming sulfide layers with certain thickness. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to analyze the phase constituents and grain size of the nanocrystallized surface layer. The surface morphologies and compositions of the sulfide layers were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray photoelectron spectroscope (XPS) was used to detect the valence states of the sulfide layers. Elemental distribution with depth was measured by augur energy spectroscopy (AES). The results show that the microstructure of the surface layer is refined to nano-grains with the grain size about 30 nm and random crystallographic orientations by SFPB treatment. The surface nanocrystallization pretreatment can significantly improve the thickness, density, and the FeS content ratio of the sulfide layers. The analysis indicates that, the enhancement in efficiency of the ion sulfurization treatment by SFPB surface nanocrystallization treatment is mainly attributed to the high-density crystal defects and the increase of surface chemical activity.

Surface nanostructure formation mechanism of 45 steel induced by supersonic fine particles pombarding

By means of supersonic fine particles bombarding (SFPB), a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel, microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Grain size increases with an increase of depth from the treated surface. Plastic deformation and grain refinement processes are accompanied by an increase in strain. Plastic deformation in the proeutectoid ferrite phases has precedence over the pearlite phases. Grain refinement in the ferrite phases involves: the onset of dislocation lines (Dls), dislocation tangles (DTs) and dense dislocation walls (DDWs) in the original grains; the formation of fine lamellar and roughly equiaxed cells separated by DDWs; by dislocation annihilation and rearrangement, the transformation of DDWS into subboundaries and boundaries and the formation of submicron grains or subgrains; the successive subdivision of grains to finer and finer scale, resulting in the formation of highly misoriented nano-grains. By contrast, eutectoid cementite phase accommodated strain in a sequence as follows: onset of elongated, bended and shear deformation under deformation stress of ferrites, short and thin cementites with a width of about 20-50 nm and discontinuous length were formed. Shorter and thinner cementites were developed into ultra-fine pieces under the action of high density dislocation and strains. At the top surface, some cementites were decomposed under severe plastic deformation. Experimental evidences and analysis indicate that surface nanocrystallization of 45 steel results from dislocation activities, high strains and high strain rate are necessary for the formation of nanocrystallites.

The Investigation of Surface Nanocrystallization of Structural Steel Induced by Supersonic Fine Particles Bombarding

The nanostructured surface layers were fabricated on a hardened and tempered chrome-silicon alloy steel and a normalized medium carbon steel by mean of Supersonic Fine Particles Bombarding (SFPB). The microstructure features in the treated surface layer were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Experimental results show the nanostructured surface layer is fabricated on both samples after SFPB treatment. The microstructure of the top surface is characterized by uniformly distributed nano-scale grains with equiaxed shape and random crystallographic orientations. The mean size of equiaxed nanocrystallites on the top surface layer is approximately 15-20nm for the SFPB treated medium carbon steel and Chrome-silicon alloy steel. During severe deformation the grain refinement in ferrite and cementite phases is observed, the cementite phases are exposed to breaking and dissolution due to mechanical alloying resulting in the formation of a supersaturated solid solution of carbon in α-Fe matrix. In the ferrite phase, the grains are refined by the process of dislocation actives and forming cell structures separated by dense dislocation walls (DDWs), as well as evolution of dislocation to subboundaries and grain boundaries.

Design of Ultrasonic Ejecting Gun Used for Surface Nanocrystallization Based on CFD

Supersonic fine particles bombarding (SFPB) is an important way to perform surface nanocrystallization. Harder the material is, higher the bombarding particles speed is needed. The gun with excellent features is premise to obtain the nano-structured layer.This paper analysed the advantages of rectangle Laval nozzle compared to annular-shape one and calculated critical structured parameters of the nozzle.Numerical simulation analysis of flow field of the nozzle at inlet temperature 300K and inlet pressure 0.25 MP, 1.0 MP, 1.7 MP and 2.5MP and velocity field of the gun with divergent-angle extended-barrel conduced by a commercial finite volume code FLUENT software of CFD; Consequently, the overall structure of the gun was optimized and determined finally. The sample of 38CrSi steel was treated by this gun. And the nano-structure layer on the surface was observed by TEM.