Strengthening Of Surface Layer Research Articles

Surface layer strengthening mechanism of 2060 aluminum–lithium alloy after shot-peening

The microstructure evolution and strengthening mechanism of materials after shot peening have always been the focus of research. In this paper, a novel coupled constitutive model was proposed to predict the depth of fine-grain of the 2060-T8 aluminum-lithium (Al–Li) alloy after shot peening. Besides, combining the numerical and experimental methods, the influences of shot size on yield stress, dislocation density, and crystal orientation of Al–Li alloy were systematically studied to reveal the strengthening mechanism. The results show that larger shot sizes can significantly improve the depth of the dislocation density layer and the fine-grain layer of 2060 Al–Li alloy. The depth of the refinement layer increases from 50 μm to 80 μm when the shot size grows from 0.3 mm to 0.6 mm. It is found the depth of the grain refinement layer in the experiment is consistent with the depth where is a sudden change of grain size in the simulation. Additionally, electron backscatter diffraction (EBSD) shows that many sub-grains are produced in the material due to high dislocation density, and the proportion of low-angle grain boundaries (LAGB) increases significantly, from 48.3% to more than 98.4%. The crystal orientation in the grain has changed obviously and Goss texture {100}<001> obtained in the deformation band. In contrast, with the increase in shot size, the proportion of the Schmid factor with a high-level trend increases. However, the hardening effect of the material is much greater than the softening effect which results in higher yield stress and microhardness of the top surface.

The 19552 Steel Forging Die Surface Layers Strenghtening

Abstract The paper briefly describes factors influencing the effectivity of forgings production. It focuses on lifetime of forging dies and possibilities of surface layers mechanical strengthening application. Included are also the results of experiments in the area of surface layer strengthening of forging die tool steels by shot peening. The article presents the results obtained on the basis of monitoring the influence of the initial hardness on the surface roughness after shot peening and on the course of hardness in the surface layer after shot peening. The results of the experiments confirmed the beneficial effect of mechanical reinforcement (strengthening) on the final properties of surface layer.

Влияние силы деформирования при поверхностном пластическом деформировании на глубину упрочнения поверхностного слоя детали

The results of investigations carried out on the impact of deformation force upon the depth of surface layer strengthening of a part are presented. There is presented a procedure of investigations carried out, the equipment used is shown. The recommendations for the choice of modes for processing with surface plastic deformation are given.

Structural phase states and properties of rails after long-term operation

The investigations into structural phase states and properties of differentiatedly quenched 100-m rails of DT 350 category after extremely long-term operation (passed tonnage of 1411 mln. t brutto) were performed by the methods of modern physical material science. It has been established that rail operation results in the essential strengthening of surface layer up to 80–100 μm in thickness independent of the studied area of rail head. The microhardness of rail surface is 1.5–2-fold higher in comparison with volume and it decreases with the distance from the surface. A 7-fold increase in wear resistance of tread surface and 1.3-fold increase in friction coefficient with respect to volume have been revealed. The values of α-Fe crystal lattice parameter of tread surface (a = 0.28699 nm), the distortions of cementite crystal lattice (Δd/d = 2.37·10-3) are higher but the relative content of cementite (3.31 mas. %) and the size of coherent-scattering region (D = 20.6 nm) are lower than the corresponding values in volume. The long-term operation of rails is accompanied by the failure of cementite plates and carbon being liberated goes into solid solution and precipitates on the defects of crystal structure (dislocations, interphase and intraphase interfaces).

Fatigue properties of welded Strenx 700 MC HSLA steel after ultrasonic impact treatment application

Ultrasonic impact treatment is a recent post weld treatment technique which can be applied to straighten the welding deformations and to increase the fatigue endurance due to the positive effect of deformation strengthening of surface layers, induction of compressive residual stresses in the sub-surface layers and decreasing the surface roughness. Ultrasonic impact treatment was applied on welded joints manufactured from Strenx 700 MC high strength low alloy steel with the aim to improve its fatigue endurance. Three different parameters of ultrasonic impact treatment were applied and their influence on the fatigue endurance was studied. Based on measurements of residual stresses in the surface and sub-surface layers, surface roughness and results of fatigue tests the optimal parameters of ultrasonic impact treatment process were determined. As a result, it was possible to increase the fatigue limit at N = 107 cycles by about 12%.

Effect of Shot Peening on the Mechanical Properties and Cytotoxicity Behaviour of Titanium Implants Produced by 3D Printing Technology.

Structural discontinuities characterize the implants produced directly from metal powders in 3D printing technology. Mainly, the surface defects should be subjected to procedures associated with surface layer modification (likewise shot peening) resulting in the increase of the implant service life maintaining optimal biocompatibility. Therefore, the purpose of the present study was to investigate the effect of type of shot used for the peening process on the Ti-6Al-4V implants functional properties as well as the biological properties. The components were produced by DMLS (direct metal laser sintering) additive technology. The surfaces of titanium specimens have been subjected to the shot peening process by means of three different shots, i.e., CrNi steel shot, crushed nut shells, and ceramic balls shot. Then, the specimens have been subjected to profilometric analysis, microhardness tests, and static strength testing as well as to the assessment of biocompatibility in respect of cytotoxicity using human BJ fibroblasts. The shot peening process causes the strengthening of surface layer and the increase of strength parameters. Furthermore, the test results indicate good biocompatibility of surfaces being tested, and the effect of shot peening process on the titanium alloy cytotoxicity is acceptable. At the same time, most favourable behaviour in respect of cytotoxicity has been found in the case of surfaces modified by means of ceramic balls > nut shells > CrNi steel shot correspondingly.

Инновационные технологии в обработке металлов давлением для транспортного машиностроения

Modern innovation technologies in metal pressure forming for transport engineering are presented. The analysis of the blank stress-strain properties impact upon parts quality is carried out. A method for thread surface layer strengthening is considered. The impact assessment of an elongation ratio and anisotropy upon ear values is carried out.

A combined surface layer strengthening of aluminum alloys by plastic deformation and vacuum ion plasma processing methods

The influence of tool effects of the processing media on formation of corrosion characteristics (reactive capacity and corrosion resistance) in the surface layer of aluminum alloys during strengthening by surface plastic deformation and vacuum ion-plasma processing has been investigated. It has been shown, by example of V95pchT2 alloy, that formation of the surface layer corrosion characteristics under the integrated effect of processing media (shot, plasma) is determined by the interaction modes of the tool/work surface contact pair. The influence of reactive capacity, which has been formed during strengthening, on changing corrosion resistance of the strengthened surface layer under the action of 5 % solution of NaCl (120 hours test base) has been considered.

Установка химико-термической обработки и ультразвукового воздействия для упрочнения поверхностного слоя стальных изделий

In connection with the intensification of operating processes, increase of tool displacement, increase of working temperatures and pressures a role of surface layer quality grows that determines an urgency for the development of new methods for its assurance. The paper reports the consideration of the plant for chemical thermal treatment and an ultrasonic impact for surface layer strengthening in steel parts.

Electrolyte-Plasma Strengthening of Surface Layers of Aluminum Alloy

Electrolyte-Plasma Strengthening of Surface Layers of Aluminum Alloy

Strengthening of surface layer of material by wave deformation multi-contact loading

It has been experimentally established that the possibility of multi-contact shock systems can transmit large total energy of the impact pulse to the deformation center. Thus, an increase in the number of instruments in a shock system from two to four, with the constant energy of the shock pulse, made it possible to increase the depth and the degree of hardening in the surface layer. The performance of multi-contact impact systems can be increased by 50% without degrading the hardening parameters by increasing the distance between the tools.

Технологические особенности формирования нанокомпозитных структур на поверхностях сложного профиля воздействием низкотемпературной плазмы

The paper reports the consideration of plasma technologies for surface layer strengthening in products, in particular, the strengthening by the impact of low-temperature plasma of the combined discharge allowing the formation of nano-composite structures in a surface layer. By the example of a cutter made of steel R6M5 there are defined basic technological peculiarities of low-temperature plasma strengthening the account of which is possible at the expense of the optimization of parameter values defining the impact of plasma upon a surface. A chart of optimum parameters of a low-temperature plasma strengthening process is obtained. There are presented results of the study of a tool surface layer strengthened with the use of a chart and also tool operation at manufacturing parts made of different materials allowing the establishment of wear resistance increase.

Heat treatment of nitrided layer formed on X37CrMoV5-1 hot working tool steel

The paper presents the technology consisting of combination of the nitriding process with subsequent austenitizing at temperature above eutectoid temperature of the Fe-C system and further rapid cooling. Such treatment will cause formation of the martensite in the area of the primarily nitrided layer and the additional precipitation hardening by tempering of heat treated steel. The article shows that the heat treatment process of nitrided layer formed on X37CrMoV5-1 steel leads to strengthening of surface layer, the substrate and the core of nitrided part. Heat treatment of nitrided steel with the tempering in inert (nitrogen) or active (ammonia) atmosphere can increase the thickness of the layer formed by short-term nitriding process. After the nitriding process of X37CrMoV5-1 steel the nitrided layer had a thickness of about 160 μm, while a subsurface layer of iron nitrides had a thickness of 7 μm. After subsequent quenching and tempering processes, the nitrided layer undergoes additional diffusion and its thickness is increased to about 220 μm (inert atmosphere) or 280 μm (active atmosphere). If the tempering process is carried out in an inert atmosphere, the primarily formed layer of iron nitrides disappears. Tempering in an active atmosphere leads to forming of white layer with a thickness of 7 μm. Basic properties of nitrided layers formed in such way, like the hardness and the wear resistance, are presented.

Specific Features of Chip Making and Work-piece Surface Layer Formation in Machining Thermal Coatings

A wide range of unique engineering structural and performance properties inherent in metallic composites characterizes wear- and erosion-resistant high-temperature coatings made by thermal spraying methods. This allows their use both in manufacturing processes to enhance the wear strength of products, which have to operate under the cyclic loading, high contact pressures, corrosion and high temperatures and in product renewal. Thermal coatings contribute to the qualitative improvement of the technical level of production and product restoration using the ceramic composite materials. However, the possibility to have a significantly increased product performance, reduce their factory labour hours and materials/output ratio in manufacturing and restoration is largely dependent on the degree of the surface layer quality of products at their finishing stage, which is usually provided by different kinds of machining. When machining the plasma-sprayed thermal coatings, a removing process of the cut-off layer material is determined by its distinctive features such as a layered structure, high internal stresses, low ductility material, high tendency to the surface layer strengthening and rehardening, porosity, high abrasive properties, etc. When coatings are machined these coating properties result in specific characteristics of chip formation and conditions for formation of the billet surface layer. The chip formation of plasma-sprayed coatings was studied at micro-velocities using an experimental tool-setting microscope-based setup, created in BMSTU. The setup allowed simultaneous recording both the individual stages (phases) of the chip formation process and the operating force factors. It is found that formation of individual chip elements comes with the multiple micro-cracks that cause chipping-off the small particles of material. The emerging main crack in the cut-off layer of material leads to separation of the largest chip element. Then all the stages of chip element formation are cycled. Fluctuations of the cutting force components completely repeat all the stages of local destruction and formation of individual chip elements. Studies have shown that with increased thickness of the cut-off layer the main crack develops below the cut-off line thus significantly affecting the quality of the machined surface: emerging cracks, cavities, chips, and other defects that significantly reduce the product performance. In machining the plasma-sprayed coatings, their high tendency to strengthening and rehardening because of the cutting action has a great impact on the surface quality. This is evident as a loss of the elastic equilibrium state stability and as a destruction of the work-piece surface layer (chipping, peeling, flaking). With increasing curvature of the machined surface (e.g., decreasing radius of cylindrical billet) the surface layer is increasingly prone to destruction. Specific problems are cutting fluids used in grinding the plasma-sprayed coatings. Machining in this case comes with saturated liquid vapours formed in the surface layer of a billet under high pressure. With a pressure drop on the tool-side in cutting there is such an intensity of vaporization that micro- and macro-fractures of the machined work-piece surface can be initiated.

In situ peeling tests for assessing the cohesion and consolidation characteristics of historic plaster and render surfaces

Standard application principles for the peeling test, also known as the scotch tape test, for assessing the surface cohesion characteristics of materials have been presented by the authors in earlier papers on laboratory testing of stone and mortar consolidation effects. The method has been in use for a long time for evaluating the strengthening of surface layers of mortars, but there have been no standards or reliably verified recommendations on how the test should be applied. Nevertheless, the method has been attracting continuing research, because it is a simple and quite reliable method for in situ testing of consolidation effects, if it is applied correctly. Our paper summarizes the basic principles, and presents illustrative results of an investigation of important historic buildings. It goes on to suggest some practical approaches and designs that are useful for in situ applications. We present a mathematical procedure suitable for evaluating the results that are obtained. We recommend repeated peeling on exactly the same place on the surface in order to compensate for and eliminate the effect of the natural decrease in the material detached from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. The examples and validation measurements presented here include in situ measurements.

Influence of the stressed state of the zone of friction contact on the formation of the structure of a surface layer and tribological properties of steels and alloys

An investigation has been performed of the influence of contact stresses, which appear in the zone of friction of iron-manganese alloys with 16.9–40.5 wt % Mn, wear-resistant high-manganese austenitic steels, and carbon steel U13, on the phase composition, structure, and strengthening of surface layers of these materials under conditions of dry friction at small (0.03 and 0.07 m/s) sliding velocities, when the frictional heating of the surface layer of the samples is virtually absent. A quantitative estimation of the arising compressive contact stresses (pressures) has been carried out. It is shown that the value of the compressive contact stresses approximately corresponds to the values of microhardness measured on the friction surface of the materials investigated. These compressive contact stresses initiate the occurrence a γ-ɛ martensitic transformation in the iron-manganese alloys with 16–40% Mn, which is characterized by a negative volume effect, but impedes the development of the ɛ-α and γ-α martensite transformations (in austenitic steels) which occur with an increase in the specific volume. The stresses in question favor the formation of nanocrystalline structures in a thin (≤10 μm thick) surface layer of friction steels and alloys. The contact tensile stresses following the contact compressive stresses initiate the formation and propagation of microscopic cracks in the surface layer of the friction materials, and activate the development of martensitic ɛ-α and γ-α transformations in this layer. It is shown that the structural and phase transformations initiated by contact stresses exert a substantial effect on the microhardness, friction coefficient, and resistance to adhesive wear of the steels and alloys under study.

Convective heat and mass transfer at the solidification front of binary alloys subjected to laser treatment

The process (initiated by convection at the melt-crystal interface) of the formation of a cellular structure at the front of rapid solidification in binary metallic alloys irradiated with a laser with a wavelength λ ∼ 1 μm at a density of radiation power q ∼ 108–1010 W/m2 and pulse duration τ ∼ 10−3 s has studied; an original physical model of convective heat and mass transfer at the melt-crystal interface under the effect of laser treatment with the above parameters has been developed; an improved mathematical formulation of the problem of stability of a planar solidification front has been suggested; formulas for calculating parameters of the process of heat and mass transfer at the melt-crystal interface are given; and experimental data on the formation of cellular structures on Grade 45 steel and some alloys such as L62 (Cu-38% Zn) and Nb-50% Ti are presented. The results of the investigation can serve as a theoretical base for controlling directionally solidified structures and properties of surface layers of metallic alloys subjected to laser treatment; in practice, they can be applied for laser strengthening of surface layers of heavily loaded friction units.