Microstructure Of Surface Layer Research Articles

Surface nanocrystallization, austenization and hardening of medium carbon steel by an explosive impact technique

An explosive impact technique was used to harden a medium carbon steel plate with a thickness of 6mm. The explosive impact produced relatively uniform microstructure and mechanical properties in the impact surface layer. The austenite equiaxed nanocrystallines were formed in this layer; the grain size and the depth respectively are 10nm and 5μm approximately. The microhardness of the impact surface was increased to 475HV from 130HV and the wear resistance was doubled. Moreover, the impact surface has a greater hardness than the explosive surface, and the hardness gradually decreased with the depth increases from both sides. The plastic deformation penetrated through the entire plate depth, the depth of highly hardening layers was arrived at 500μm and a sandwich structure was produced. By the server plastic deformation, the cementite flakes appeared slip, segmentation and the fracture. Comparing with the surface severe plastic deformation (SPD) processes, the explosion impact has a stronger ability for hardening the entire plate depth and a little weaker surface strengthening effect. The nanocrystallization, austenization and hardening mechanisms were discussed.

Experimental Study of the Influence of Shot Peening on the Microstructure and Properties of Surface Layer of a TC21 Titanium Alloy

The effects of shot peening on microstructure and properties of surface layer of a TC21 titanium alloy have been studied by transmission electron microscopy, electron back-scattered diffraction, X-ray diffraction and Nano-indentation. The results indicated that an elastic-plastic strengthening layer was formed on the surface of the TC21 alloy after the shot peening. During the deformation processing, the activated slip systems were found to be in <a>, <c> and <a/c> planes with high-density dislocations formed as networks in α phase. After the shot peening, the residual stress was found in the strengthening layer, which decreased from the surface to the interior, and the thickness of the surface layer was measured about 370 μm. The hardness by nano-indentation measurement increased two times as compared with the original material. After the shot peening, the fraction of the low-angle boundaries between 0-10º was estimated as 59.3% at the depth of 100 μm from surface. This surface layer microstructure improved resistance of deformation of the TC21 alloy, and therefore increased its fatigue strength.

Microstructure and mechanical properties of surface layer of M50NiL steel plasma nitrided

The quenched M50NiL steel specimens have been plasma nitrided at temperatures from 460 to 590°C for 4 h under a constant mixture gaseous supply of 0·05N2–0·4H2 L min−1. The effects of the treatment temperature on the microstructure, microhardness and wear resistance of the surface nitrided layers are studied. The results show that the plasma nitrided layer includes only the diffusion layer without conventional compound layer. The surface hardness is significantly enhanced. α′-Fe and γ′-Fe4N phases in surface layer are formed at relatively low nitriding temperatures (460–560°C), while a low nitrogen phase FeN0·076 forms when the nitriding temperature exceeds 575°C. With the increase in nitriding temperature, the nitrided layer thickness increases, whereas both the surface and core microhardness of the nitrided specimens decreases. The wear resistance of specimens can also be improved significantly by plasma nitriding.

Effective Duration of Gas Nitriding Process on AISI 316L for the Formation of a Desired Thickness of Surface Nitrided Layer

High temperature gas nitriding performed on AISI 316L at the temperature of 1200°C. The microstructure of treated AISI 316L samples were observed to identify the formation of the microstructure of nitrided surface layer. The grain size of austenite tends to be enlarged when the nitriding time increases, but the austenite single phase structure is maintained even after the long-time solution nitriding. Using microhardness testing, the hardness values drop to the center of the samples. The increase in surface hardness is due to the high nitrogen concentration at or near the surface. At 245HV, the graph of the effective duration of nitriding process was plotted to achieve the maximum depth of nitrogen diffuse under the surface. Using Sigma Plot software best fit lines of the experimental result found and plotted to find out effective duration of nitriding equation as Y=1.9491(1-0.7947 x ), where Y is the thickness of nitrided layer below the surface and X is duration of nitriding process. Based on this equation, the duration of gas nitriding process can be estimated to produce desired thickness of nitrided layer.

The microstructure of Si surface layers after He+ Ar+plasma immersion ion implantation

Processes accompanying the amorphization of Si surface layer after Ar+ and He+ low energy plasma immersion ion implantation were studied by transmission electron microscopy and microanalysis. The ion energies varied in the range of 0.5 – 3 keV with the doses of 5·1015 cm−2 for Ar+ and 2·1016 cm−2 for He+ pre-amorphization implants. A perturbation of Si lattice together with porosity was found. The utilization of heavy and light ions causes distinctive microstructural peculiarities. The presence of oxygen and its distribution near the surface layer was determined by electron energy loss spectroscopy.

Chromium oxide dissolution in steels via short pulse laser processing

Changes of microstructure, chemical and phase compositions in thin surface layers of low carbon steel saturated by chromium oxide have been studied by TEM, XPS and XRD methods. Ultrafine chromium oxide powder was spread on a steel surface and subjected to laser processing with nanosecond pulses. It was found that such conditions of processing as overheating of small volume of metal, high temperature gradient, rapid solidification and laser-induced plasma formation lead to dissolution of chromium oxide in the metal matrix. As a result of laser processing the surface layers contain chromium oxide, chrome-spinel FeO $$\cdot $$ Cr $$_{2}$$ O $$_{3}$$ and chromium in metal state dispersed in alpha and gamma iron. The processing technique allows to obtain surface layers whose chemical composition might be equivalent to the composition of stainless steels.

Fe–15 wt-%Cr–X wt-%C hardfacing surface layer: wear resistance and its enhanced mechanism with C additive

An electrode with different C additives was developed. The microstructure of the hardfacing surface layer was observed by optical microscopy. The phase structure was determined by X-ray diffraction. The hardness and wear resistance of the hardfacing surface layer were measured respectively. The worn-out surface and three-dimensional morphology were observed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometry. The relation curve between mass fraction of M7C3 carbide and temperature was calculated according to thermodynamics software Thermo-Calc. The results show that, with the increase in C additive, the hardfacing surface layer changes from a hypoeutectic structure to a hypereutectic one. Meanwhile, the primary phase changes from austenite to carbide. The hardness and wear resistance of the hardfacing surface layer increase gradually with the increase in C additive, and when the C additive is 25 wt-%, they are the largest. With the increase in C content, the precipitation temperature of M7C3 decreases from 1280 to 1260°C, while the maximum amount of M7C3 increases instead, which is from 0·154 to 0·313. The reason of the improvement for wear resistance of the hardfacing surface layer is that the carbide initiates and the amount of M7C3 increases.

Microstructural features and orientation correlations of non-modulated martensite in Ni–Mn–Ga epitaxial thin films

Epitaxially grown thin films with nominal composition Ni50Mn30Ga20 and thickness 1.5μm were prepared on MgO(100) substrate with a Cr buffer layer by DC magnetron sputtering. The surface layer microstructures of the as-deposited thin films consist of non-modulated (NM) martensite plates with tetragonal structure at ambient temperature, which can be classified into the low and high relative contrast zones of clustered plates (i.e. plate colonies) with parallel or near-parallel inter-plate interface traces in secondary electron images. Orientation analyses by electron backscatter diffraction revealed that individual NM plates are composed of alternately distributed thicker and thinner lamellar variants with (112)Tetr compound twin relationship and coherent interlamellar interfaces. In each plate colony, there are four distinct plates in terms of the crystallographic orientation of the thicker lamellar variants and therefore, in total, eight orientation variants. For the low relative contrast zones, both thicker and thinner lamellar variants in adjacent plates are distributed symmetrically across their inter-plate interfaces (along the substrate edges). At the atomic level, there are no unbalanced interfacial misfits and height misfits, resulting in long and straight inter-plate interfaces with homogeneous contrast. However, in the high relative contrast zones, the thicker and thinner lamellar variants in adjacent plates are oriented asymmetrically across their inter-plate interfaces (at ∼45° to the substrate edges). Significant atomic misfits appear in the vicinity of the inter-plate interfaces and in the film normal direction. The former result in bending of the inter-plate interfaces, and the latter give rise to the high relative contrast between adjacent plates.

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.

Structural-phase changes in surface layers of elements made of VT6 titanium alloy under irradiation by high-current pulsed electron beam

Transmission electron microscopy (TEM), optical metallography, and electron probe microanalysis (EPMA) were used to study the chemical composition and microstructure of surface layers in blades made of VT6 alloy treated by a high-current pulsed electron beam at the energy density of the beam W = 18–20 J/cm2. It is shown that the melting regime of irradiation leads to formation of a high-strength surface layer of up to 25 μm in thickness with a fine substructure. The increase in mechanical properties of the modified layer is caused by formation of fine α′- and α″-martensite plates oriented almost parallel to the blade surface.

Microstructure and corrosion resistance of quenched AISI 4140 steel plasma nitrided and nitrocarburised with and without rare earths

The quenched AISI 4140 steel specimens have been pulse plasma nitrided and nitrocarburised with and without rare earth addition at 560°C for 4 h. The microstructure, microhardness and corrosion resistances of surface layers for the nitrided/nitrocarburised specimens were characterised using optical microscopy, X-ray diffraction, microhardness test, scanning electron microscopy and anodic polarisation tests in 3·5%NaCl solution respectively. A significant hardened layer bearing compound and diffusion layer can be obtained when the quenched steel (α′-Fe) is plasma nitrided/nitrocarburised at this experimental condition, and the compound layer mainly consists of γ′ (N/N,C) and ϵ (N/N,C) phases. The results show that the rare earth addition favours the formation of ϵ (N,C) phase in the surface layer. The compact compound layer with more ϵ (N,C) phase can be obtained by plasma rare earth nitrocarburising of the quenched AISI 4140 steel and has much higher corrosion potential, pitting potential and longer passive region than other compound layers.

Analysis of microstructure of surface layer of a hole while deforming drawing in lubricants

The influence of applied lubricants on formation of a surface layer microstructure while deforming drawing for various materials and technological parameters is considered in this article.

Transformations of Phases in Titanium Alloy after High Temperature Hydrogen Treatment

Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy and titanium Grade 3. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650°C, a cyclic hydrogen-treatment (3 cycles 850 °C to 250 °C) and a dehydrogenation in vacuum (550°C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this work is to determine the effect of hydrogen on the two-phase microstructure in Ti-6Al-4V alloy and Grade 3 titanium and hardness after high temperature hydrogen treatment.

Study of microstructure of surface layers of low-carbon steel after turning and ultrasonic finishing

Profilometry and optical and transmission electron microscopy are used to examine the microstructure of surface layers of a low-carbon ferrite-pearlite steel subjected to turning and ultrasonic finishing. It is shown that turning peaks and valleys have different microstructures, which stipulates manifestation of technological hereditary when processing surfaces of machined parts. Ultrasonic finishing causes the severe plastic deformation of the surface layer, which favors the elimination of a technological heredity that is acquired during turning.

3D-FE-Modelling of the Drilling Process – Prediction of Phase Transformations at the Surface Layer

Due to friction, plastic deformation and cutting, the drilling process leads to high mechanical and thermal loadings of drilling tool and workpiece. Distortion and modifications of the surface layer microstructure, especially rehardened zones, can be observed, whereby the experimental investigation of correlations between machining processes and resulting surface layers are very complicated and time consuming. This paper presents a numerical approach to predict machining induced phase transformations at the surface layer of drilled holes. Based on experimental results and 2D FE machining simulations, an abstract model representing the mechanical and thermal collective load of the drilling process has been developed in relation to the parameters cutting speed and feed rate. To predict phase transformations of the steel 42CrMo4 (AISI 4140) at the surface layer of drilled holes a 3D FE- model has been established using the commercial software ABAQUS. The kinetics of the phase transformations are implemented using specific user subroutines. The model calculates the process of austenization and the transformed volume fraction of the phases ferrite/perlite, bainite and martensite and also considers transformation plasticity and the resulting hardness of the microstructure. By simulating different combinations of cutting parameters, relations between drilling process and resulting surface layers of drilled holes have been studied. In addition the machining induced distortion of the workpiece can be calculated simultaneously. The simulation model has been verified by drilling experiments, thermal imaging and metallographic investigations. Predicting machining induced surface layer states, the functionality of future components can be improved.

The Anti-fatigue Mechanisms on Alterations of Structures and Performances of Alloy Welded Joints with Ultrasonic Impact Treatment

The specimens of aluminum alloy welded joint were prepared by gas tungsten arc welding using 2A12 sheets and ER5356 welding wires. Some specimens were full coverage strengthened by ultrasonic impact treatment and the others were not strengthened. The surface layer microstructures of the ultrasonic impact treated and untreated specimens were investigated by optical microscopy and transmission electron microscopy. The surface layer hardness and residual stress distributions along the thickness direction were measured by micro-hardness tester and X-ray diffraction method. The results showed that a grain refinement layer which depth extended up to about 150∼200 μm was produced by ultrasonic impact treatment. The average hardness value of the treated specimens was up to 110 HV, increasing by 45% compared with 76 HV of the untreated specimen. A residual compressive stress layer was also produced by ultrasonic impact treatment, and the depth was close to 900 μm. The maximum residual compressive stress was -285 MPa. At the same time, the anti-fatigue mechanisms on grain refinement, work hardening and residual compressive stress of aluminum alloy welded joint with ultrasonic impact treatment were also discussed.

Surface Remelting of Multi-Phase Sintered Steel

This study presents the results of the investigations of the effect of surface remelting using arc welding (GTAW) on the microstructure and selected properties of surface layer of sintered steels 304L and 434L. It was found that in order to improve surface quality in these sinters, remelting should be carried out at lower current intensities, i.e. 30A and 40A. The surface treatment carried out in the study allowed for obtaining an uniform cellular-dendritic microstructure in surface layer. X-ray examinations demonstrated the effect of compressive stress in surface layer, which reduces the risk of cracking on the surface.

Microstructure and mechanical properties of surface layers of 30CrMnSiA steel plasma nitrocarburized with rare earth addition

The pulse plasma nitrocarburizing for 30CrMnSiA steel was conducted at 560 °C for 8 h in mixed gases of N2:3H2 and different flow rates of rare earths (RE) addition. Effects of rare earths (RE) addition in the carrier gas on the surface morphology, phase structure and mechanical properties of the nitrocarburized layer were characterized by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing and wear testing, respectively. The results showed that the surface phase structures changed from dual phases ɛ-Fe2-3N(C) and γ′-Fe4N(C) to phase Fe3C and incipient nitrides, and the nitrocarburized surface hardness value decreased slightly from 756 to 681 HV0.1 with the RE addition increasing in the carrier gas, and the corresponding morphology of the nitrocarburized surface was granular nitride group (diameter 0.8–1.5 μm) and compact-fine Fe3C stick and patch (mean size 100–300 nm), respectively. The wear resistance of the experimental steel could be improved remarkably by plasma RE nitrocarburizing. The nitrocarburized layer with Fe3C phase formed in the mixed gases of N2:3H2 and flow rate of 0.5 L/min RE addition showed the lowest friction coefficient and the narrowest wear track.

Nanostructure Layer Formation on Cu-Zr-Al Alloy during Laser Remelting

This paper reports laser remelting of crystalline Cu based alloys in order to produce amorphous layer on the surface. The as prepared Cu based master alloy ingots were imbedded in a metallic sinking with Wood metal to assure the good thermal conductivity during the laser treatment. The laser remelting of a thin surface layer and a subsequent rapid cooling of it was performed using impulse and continuous mode of Nd:YAG laser. In respectively the impulse mode the laser power and the interaction time were 1.5; 2 kW and 20÷100 ms. In the continuous mode the laser power was 2 kW, and the laser scan speed was 80÷120 mm/s. The characterization of the microstructure of surface layer was performed by XRD, scanning electron microscopy and microhardness measurements.

The microstructure of surface layers of 6khs steel knives

Наведені результати мікроструктурного аналізу поверхневих шарів деревообробних ножів після експлуатації протягом дев'яти місяців зі сталі 6ХС. Запропоновані можливі варіанти відновлення та покращення різальних властивостей виробів.