Plastic Deformation Of Surface Layer Research Articles

INFLUENCE OF PULSED BEAM-PLASMA IMPACTS ON THE STRUCTURAL CHARACTERISTICS AND MECHANICAL PROPERTIES OF THE SURFACE LAYER IN INCONEL 718 ALLOY

The results of studying the effects of pulsed flows of helium ions (HI) and helium plasmas (HP) on the Inconel 718 alloy prepared by additive technology by selective laser melting followed by heat treatment are presented. The main structural changes in the irradiated surface layer (SL) are determined for two modes of irradiation - soft (with radiation power density q = 2 ∙108 W/cm2 at pulse duration τ = 50 ns) and hard (at q = 1.5 ∙109 W/cm2, τ = 25 ns). The number of pulsed actions in each mode was N = 10 and 20. It has been found that in the initial state and after irradiation, the alloy under study is a single-phase nickel-based solid solution with an fcc lattice. The impact on the alloy of pulsed HI and HP flows leads to a change in the initial texture in the 220 direction to texture 111. This change in the texture favored the occurrence of the plastic deformation (PD) process observed in the irradiated SL, during which in metals with an fcc lattice, under the action of applied thermal stresses, slip occurs predominantly along the {111} planes. The influence of the irradiation mode of the investigated alloy on the parameter of its crystal lattice is noted. In the soft mode of exposure to HI and HP flows, the lattice parameter a decreases compared to the initial value, which may be due to the action of residual macrostresses, as well as to the evaporation of atoms of impurity elements located in lattice interstices from the SL. In the hard irradiation regime, the parameter a increases, which is due to the dominant influence of the mechanism of implantation of helium ions into the alloy, which contributes to the increase in the value of a. It have been shown that the observed structural changes in the SL of the alloy lead to a decrease in microhardness and softening of the remelted layer. The role of thermal and shock-wave effects in the processes of PD and structural changes in SL under the implemented irradiation conditions was estimated by numerical simulation.

Functionally oriented high-temperature composite materials

The authors developed technology for obtaining surface composite materials. This technology includes high-energy mechanical treatment, high-velocity oxygen fuel spraying in a protective atmosphere and subsequent thermomechanical and thermal treatment of ZrCuNiCoTi and cBNNi3AlSiCCoY layers in a protective atmosphere. The processing allowed increasing the adhesive strength of the surface composites, reducing their porosity and improving their functional and operational properties. Staged methods of heat treatment and plastic deformation of surface layers have been developed. These methods stabilize the material structure while reducing residual stresses. On the basis of complex X-ray diffraction and electron microscopic studies, the structural parameters of surface composites were determined. It was shown that the ZrCuNiCoTi alloy is in the austenitic–martensitic state and has a nanocrystalline structure with a grain size of 80–120 nm. Meanwhile, the cBNNi3AlSiCCoY alloy consists of many intermetallic phases and inclusions and has a nanosized structure with a grain size of 100–200 nm. A microhardness study of the surface layers in ZrCuNiCoTi–cBNNi3AlSiCCoY composite showed that thermomechanical treatment increases microhardness. The experimental data were statistically processed. As a result, empirical mathematical dependences of the stress amplitude on cyclic durability were compiled. Mechanical tests included tests of NiCoTiZrHf–cBNCoMo, ZrCuNiCoTi–cBNNi3AlSiCCoY and TiNiZrHfCoCu–cBNCoNiAlY composites for multi-cycle fatigue during bending with rotation.

Mechanisms of crack generation in high-pure tungsten exposed to high power density plasma

The mechanisms of crack formation in the tungsten divertor plates irradiated by hydrogen plasma under ITER-type steady-state and transient events are investigated. The stresses and defects of samples‘ initial structure are annealed as a result of steady-state irradiation with Falcon ion source, which generates 2 keV hydrogen ion flux of ~ 1022 m-2s−1 and power density ~ 1.7 MW × m−2. Quasi-stationary plasma accelerator QSPA Kh-50 provides pulsed hydrogen plasma loads which operating mode simulates transient events (type I ELMs) in ITER: ion impact energy is about 400 eV, maximum plasma pressure is 0.32 MPa, pulse duration is 0.25 ms. The diffraction maxima profiles, positions, intensities, half-widths, and intensity distributions are analyzed. The origin of crack formation is found to be in the plastic deformation of surface layers by the twinning mechanism. The latter is reinforced by the interaction of twins with the hydrogen-filled micro-pores. The micro-pores appear as a result of hydrogen saturation of subtraction loops formed due to the coalescence of vacancy complexes.

Influence of reinforcing plastic surface deformation on surface performance of machine parts

The performance of the machines part reinforcement using surface plastic deformation shall be considered as formation of the whole complex of surface parameters and quality and their impact on the operational properties of these parts. The main surface quality parameters, affecting the performance of machine parts are geometric (microgeometry, wavelength, roughness, shape of inequalities, the size of the supporting surface, the direction of the traces of processing); physical parameters (structure, degree and slander depth, residual stresses in the surface layer). In the machine building, many methods of superficial plastic deformation are used for part reinforcement; these methods essentially differ in the scheme of impact of the surface deforming part to be treated. After analyzing the results obtained by scientists, involved in research on surface plastic deformation of surface layers and surfaces of parts, it was found that after hardening, practically all structural changes contribute to reinforcement of the surface layer material and increase the plastic deformation resistance. Increasing the density of dislocations and the separation of carbides, which block the shear slides and create obstacles to the movement of dislocations. Due to these changes, resistance to formation and spread of fatigue cracks have increased. The treatment depth, magnitude of residual stresses and increase in hardness depends on the original structure and chemical composition of the material. Reinforcement regimes have significant effects on the wear resistance. Use of diamond smoothing, vibration processing, combined methods (surface plastic deformation in combination with other reinforcement methods, as well as the use of a combined tool) opens up new possibilities for increasing the quality characteristics of the surface and the surface layer of parts, and accordingly, increasing their operational properties with all the diversity and complexity of used processes. Based on the results of the studies, practical recommendations on the application of methods of hardening by surface plastic deformation of machine parts and a methodology for designing technological processes for their manufacture considering manufacturing capabilities are proposed.

Microstructure and mechanical properties of CP-Ti subjected to UIT

The ultrasonic impact treatment (UIT) effect on microstructure and mechanical properties of commercial purity titanium (CP-Ti) was studied. The microstrucrure was investigated by X-ray diffraction analysis and optical profilometer New View 6200. The microhardness of CP-Ti specimens was measured by microhardness tester with the Vickers pyramid. It was found that UIT of CP-Ti specimens led to severe plastic deformation of surface layer with a thickness equals to 120 μm. This was accompanied by an increase in compressive residual stresses, a growth of the microhardness, a crystallographic texture change and a rise of density of deformation twins in surface layers of titanium specimens. It was shown that the deformation twins play a determining role in microstructure and mechanical properties changes of the surface layer of titanium specimens.

Plastic deformation of surface layer by sliding elliptical cylinder

Steady-state plastic deformation of the workpiece surface layer by sliding of the elliptical rigid cylinder is simulated. The plane-strain theory of an ideal plastic solid with consideration of Prandtl’s contact friction is used. Contact pressure distribution and form of the plastic region are defined by the steady-state plastic flow condition. Significant effects of contact boundary curvature variation and contact friction on the distribution of contact pressure and the plastic deformation of a workpiece surface layer have been found.

Plastic deformation of surface layer during rigid cylinder rolling and sliding

Steady-state plastic deformation of the surface layer induced by the rolling and sliding of a rigid cylinder is investigated using ideal plastic plane strain theory taking into consideration contact friction. The plastic region and length of the contact arc related to the forces and the moment applied to the cylinder are calculated. Results are studied for rolling friction theory in the case of large contact loads and for surface plastic-layer deformation to increase the wear resistance and fatigue strength of machine parts.

Effect of cold work on surface reactivity and nano-hardness of alloy 800 in corroding environments

In this paper, in situ scanning electrochemical microscopy (SECM) was used to investigate effect of cold work on surface reactivity of UNS N08800 alloy, and in situ nanoindentation technique was employed to measure corrosion-induced degradation of resistance to plastic deformation in surface layer. The SECM measurements indicated that cold work would cause an increase of surface reactivity, especially on surface area around non-inclusions. According to in situ nanoindentation measurements, anodic dissolution would reduce the surface hardness. This effect was enhanced by cold work.

The effect of PVD coatings on the tensile strength and low-cycle fatigue resistance of stainless steel and titanium alloys

PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5-μm-thick PVD coatings of TiN, Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT-81556A and (10-2-3; 4966) on their tensile strength and low-cycle fatigue resistance when the development of large elastic–plastic strains takes place. The tensile and low-cycle fatigue tests were conducted under conditions of axial zero-to-tension cycle of the stress-controlled loading on flat 1- to 1.5-mm-thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low-cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low-cycle fatigue resistance in the quasi-static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53–86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.

The Research on Cylindrical Ultrasonic Rolling Machining Used for Strengthening Metal Surface

Material mechanics and dynamic properties affect the service life of parts, and also the normal operation of machines. In order to reduce the processing time and improve the quality of machining, a cylindrical roller was used in the research. Cylindrical ultrasonic rolling machining (CURM) is an efficient way to enhance the service properties and surface characteristics of components. CURM was designed and later tested on the 45# steel surface. The result showed that the plastic deformation of surface layer was symmetrical and the surface grain was reduced in size by approximately 4.2%. The result of the experiment showed that CURM was effective in enhancing the productivity as well as enlarging the yield strength and hardness of components.

Erosion–corrosion of carbon steel in simulated tailing slurries

This paper investigates the synergism of mechanical and electrochemical factors in erosion–corrosion. The fact that active corrosion in the tailing slurry donates a small portion of total material loss indicates that the synergism results mainly from corrosion-enhanced erosion. As theoretically predicted, the erosion rates in corroding slurry under same hydrodynamic condition is a linear function of logarithmic corrosion rate, suggesting that the corrosion-induced surface plasticity is the dominate mechanism of corrosion-enhanced erosion. The reduced resistance to plastic deformation in surface layer while exposed to corroding media is demonstrated by the in situ micro-hardness measurements. The erosion-enhanced corrosion in flowing slurry of steel is a result of dynamic plastic deformation caused by erodent impingement.

Dry sliding wear behaviour of magnesium alloy based hybrid composites in the longitudinal direction

In the present investigation, the wear behaviour of a creep-resistant AE42 magnesium alloy and its composites reinforced with Saffil short fibres and SiC particles in various combinations is examined in the longitudinal direction i.e., the plane containing random fibre orientation is perpendicular to the steel counter-face. Wear tests are conducted on a pin-on-disc set-up under dry sliding condition having a constant sliding velocity of 0.837 m/s for a constant sliding distance of 2.5 km in the load range of 10–40 N. It is observed that the wear rate increases with increase in load for the alloy and the composites, as expected. Wear rate of the composites is lower than the alloy and the hybrid composites exhibit a lower wear rate than the Saffil short fibres reinforced composite at all the loads. Therefore, the partial replacement of Saffil short fibres by an equal volume fraction of SiC particles not only reduces the cost but also improves the wear resistance of the composite. Microstructural investigation of the surface and subsurface of the worn pin and wear debris is carried out to explain the observed results and to understand the wear mechanisms. It is concluded that the presence of SiC particles in the hybrid composites improves the wear resistance because these particles remain intact and retain their load bearing capacity even at the highest load employed, they promote the formation of iron-rich transfer layer and they also delay the fracture of Saffil short fibres to higher loads. Under the experimental conditions used in the present investigation, the dominant wear mechanism is found to be abrasion for the AE42 alloy and its composites. It is accompanied by severe plastic deformation of surface layers in case of alloy and by the fracture of Saffil short fibres as well as the formation of iron-rich transfer layer in case of composites.

Investigations on the Effect of Ball Burnishing Parameters on Surface Roughness and Corrosion Resistance of Hsla Dual - Phase Steels

Surface finish has a vital influence on most functional properties of a component, such as fatigue strength, wear resistance and corrosion resistance. This has led to processes such as lapping, honing, and burnishing. Burnishing is a fine finishing operation involving the cold working and plastic deformation of surface layers to enhance the surface integrity and the functional utility of a component. This study has been carried out to establish the effect of burnishing parameters, i.e. feed rate, speed, force, ball diameter and lubricant on surface roughness and corrosion resistance of HSLA dual – phase steel specimens. The result indicates that burnishing parameters have a significant effect on surface roughness and corrosion resistance. Keywords: Hardness; Burnishing; Factorial Design; Inter-Critical Temperature East African Journal of Sciences Vol. 2 (2) 2008: pp. 164-169

Investigations on the Effect of Ball Burnishing Parameters on Surface Hardness and Wear Resistance of HSLA Dual-Phase Steels

Surface finish has a vital influence on most functional properties of a component like fatigue life, wear resistance, corrosion resistance, etc. This has given birth to processes such as lapping, honing, burnishing, etc. Burnishing is a fine finishing operation involving the cold working plastic deformation of surface layers to enhance the surface integrity and the functional utility of a component. The present study has been carried out to establish the effect of burnishing parameters viz. feed rate, speed, force, ball diameter and lubricant on surface hardness, and wear resistance of HSLA dual-phase steel specimens. The result indicates that burnishing parameters have significant effect on the surface hardness and wear resistance.

Improvement of wear resistance of hot working tool steel by hardfacing Part 2 – Case study

The performance and service life of the die components are limited because of different reasons such as thermal and mechanical fatigue cracking, wear, plastic deformation, etc. To minimise these damages, the dies are normally subjected to a variety of surface engineering processes. In the present study, the dimensional loss and lifetime of hardfaced and unmodified H11 steel hot forging dies were monitored during service and compared. For this purpose, various experimental tools such as XRD, SEM, optical metallography and microhardness test were employed. Microhardness profiles from surface to the depth of the dies after service were determined to study the variations in mechanical properties. It was observed that the hardfacing with Stellite 21 and Inconel 625 alloys leads to an increase in wear resistance and the working life of the dies in industrial scale. In the case of hardfaced dies, the work hardening of surface produces a self-protecting layer which has a strong metallurgical bonding to the substrate and thus enhances more resistance to further wear, while hardness reduction during service in unmodified H11 steel die causes a reduction in wear resistance and plastic deformation of surface layer.

Effect of tangential load on the stressed state of rubbing rough bodies

Formulae for the estimation of any stress tensor component at some point in an elastic half-space are presented. With these formulae, the normal and maximum tangential stress distributions in the deep layers are studied in detail. The sinusoidal indenter may be used as a model for surface roughness. Some suppositions about possible destruction mechanisms of conjugate bodies under frictional contact are suggested. Surface roughness causes deep plastic deformation of surface layers. With rough surfaces high frequency oscillations occur and even with low sliding velocities the oscillations may achieve high frequencies.