Results Of Microhardness Measurements Research Articles

About the Effect of Residual Stresses on Microhardness Readings

For steel samples made of S690QL the influence of residual stresses on microhardness is systematically investigated using a combined application of universal hardness measurements and residual stress analysis by X-ray diffraction. Measurements were carried out on a path along the bending height on the side face of a bending bar exposed to 4-point-bending (Fig.1). Elasto-plastic bending causes an inhomogeneous deformation of the steel specimen and hence results in a characteristic macro- and microresidual stress distribution. By the use of a 4-point-bending device, which can be mounted both on the hardness testing machine as well as on the X-ray diffractometer, in-situ measurements up to an elasto-plastic loading of the material enabled to distinguish between the effects of loading stresses, residual stresses and strain hardening on hardness. Loading as well as residual stresses have a marked influence on the results of microhardness measurements. This effect overlaps with consequences of strain hardening and influences characteristic hardness distributions as a function of the bending height of the bar.

Untersuchungen zum Ermüdungsverhalten der Aluminiumlegierung AA 6013 T6 in korrosivem Medium / An Investigation of the Fatigue Behaviour of the Aluminium Alloy AA 6013 T6 in a Corrosive Medium...

The aluminium alloy AA 6013 T6 is considered to be a possible alternative for the alloy AA 2024 T3 used currently in aircraft construction. In order to prove the material for use, an extensive series of tests were carried out to establish the fatigue behaviour of the material compared with that used currently. The materials were tested both in air and in artificial sea water. Specific metallographical investigations of the area surrounding the crack tip of specimens of the alloy AA 6013 T6 fatigue tested in simulated sea water revealed that the presence of hydrogen contributed significantly to the damage of the material. The presence of coarse precipitates is shown to play an important role in this process. Under cyclic loading in a corrosive medium the interface between the matrix and these particles is found to undergo significant changes resulting in the initiation of cracks emanating from the particles and their subsequent fracture. If the number of particles is plotted against the loading frequency used in the fatigue tests a surprising dependency is discovered. The results of micro-hardness measurements and investigations into the hydrogen absorption are also found to exhibit a similar frequency dependency. The corrosion mechanism taking place during cyclic loading in a corrosive medium is discussed and found to correlate well with the processes occuring during crevice corrosion.

Synthesis, microstructure and properties characterization of disintegrated melt deposited Mg/SiC composites

In the present study, elemental and silicon carbide reinforced magnesium materials were synthesized using an innovative disintegrated melt deposition method followed by hot extrusion. Microstructural characterization studies revealed the presence of minimal porosity and completely recrystallized matrix in all the unreinforced and reinforced samples. In the case of reinforced magnesium samples, a fairly uniform distribution of SiC particulates and good SiC-Mg interfacial integrity was realized. The results of microhardness measurements revealed an increase in the brittleness of the SiC-Mg interfacial region with an increase in the amount of SiC particulates. Results of physical and mechanical properties characterization revealed that the increasing presence of SiC particulates led to an increase in hardness and elastic modulus, does not affect 0.2% yield strength and reduces the ultimate tensile strength, ductility, work for fracture and coefficient of thermal expansion. An attempt is made to correlate the results of physical and mechanical properties testing with that of the microstructural characterization.

Microhardness study of (1-x-y)(B2O3)-x(Li2O)-y(MCI2), (M=Cd, Zn) glasses

Results of microhardness measurements on (1-x-y)(B2O3)-x(Li2O)-y(MCI2), (M=Cd, Zn) glasses, in the applied load range 25–500 g, are presented. The microhardness was found to decrease with increase in load up to 50 g, then it increased and finally attained a practically constant value with increase in load. The effects of composition of the glasses on microhardness are discussed.

Structural and phase transformations in Ni3Fe during high-dose ion implantation

The results are given for experimental studies of the structural-phase state formed in the surface and nearsurface layers of a disordered polycrystalline Ni3Fe alloy during high-dose ion implantation. The studies used Auger electron spectroscopy, transmission electron microscopy, x-ray structural analysis, and microhardness measurements. The ion implantation was done using the “Raduga” vacuum arc source with a multicomponent cathode of composition Zr (89.5 wt. %)+C+N+O with an acceleration voltage of 50 kV. The implanted ion dose was varied in the range (6.0·1016–6.0·1017) ions/cm2. It was established that in the surface layer which is alloyed during ion implantation there is amorphization with simulataneous formation of finely dispersed ZrO2 particles whose dimensions increase with increasing implanted ion dose; this is accompanied by an increased internal mechanical stress. Beyond the ion-implanted layer a sublayer about 10 μm thick with a high dislocation density is formed (the “long-range action” effect). The results of microhardness measurements correlate with the data from structural studies.

Indentation-induced microhardness and dielectric studies of flux-grown gadolinium aluminate crystals

Results of microhardness measurements and dielectric studies carried out on flux-grown single crystals are presented. Load independent values of hardness are estimated for (110) and (001) planes by applying the law of Hays and Kendall. The values of fracture toughness and brittleness index are calculated for median cracks at higher loads. Hardness anisotropy for both the crystal planes considered is reported. The dielectric constant, dielectric loss and conductivity are found to be dependent on temperature as well as frequency of the applied a.c. field. The anomalous behaviour of dielectric constant against temperature suggests some transition taking place at .

Microstructural gradients in thin hard coatings—tailor-made

Microstructural modifications resulting from time dependent variations of the bias voltage during the deposition of thin hard coatings are discussed. TiN-coatings are produced by reactive magnetron sputtering in several modes: (a) stepwise increase of the bias voltage during the deposition, (b) alternating sputtering with and without substrate voltage and (c) pulsed bias voltage. On the basis of X-ray diffraction measurements , it is demonstrated that residual stress gradients and texture gradients can be designed tailor-made. Furthermore, results of microhardness measurements and scratch tests indicate an improvement of the mechanical properties , especially for the application of a pulsed bias voltage.

Assessment of bond interface in impact spot welding

Results of an investigation on weld interfaces of impact-welded dissimilar metal combinations are presented. Polymeric projectiles of various nose shapes are utilized at an average impact speed of 750 m/s. It is found that welded interfaces generally comprise wavy and plane zones. Areas adjacent to waves contain hardened and plastically deformed regions. Quantitative data is presented on the composition of copper/brass interfaces. Results of microhardness measurements on copper/brass, titanium/brass and zirconium/brass weld interfaces are provided. Measurements on the local plastic thinning of the flyer plate (FP) are furnished. Effects of standoff distance (SD) and FP thickness on interface characteristics are investigated.

Load and directional effects on microhardness and estimation of toughness and brittleness for flux-grown LaBO3 crystals

Results of microhardness measurements on (100) and (110) planes of flux-grown LaBO3 crystals, in the applied load range of 10–100g, are presented. The microhardness was found to decrease with increasing load in a non-linear manner. By applying Hays and Kendall's law, the materials resistance pressure and other constants of the equation could be calculated. Hardness anisotropy, showing periodic variation of H v with the maxima and minima repeating at every 15° change in orientation of the indentor, is described and discussed. H max/Hmin are estimated as 1.14 and 1.06 for (100) and (110) planes, respectively. The fracture toughness values, K c, determined from measurements of crack lengths, are estimated to be 1.6, 1.7 MN m−3/2 (for (100) planes) and 1.2, 1.5 MN m−3/2 (for (110) planes) at 90 and 100g loads, respectively. The brittleness index, B i, is estimated as 4.6, 4.0 μm−1/2 (for (100) planes) 6.0, 4.6 μm−1/2 (for (110) planes) at 90 and 100g, loads respectively.

Thermal stresses in the tungsten and molybdenum surface layer following laser treatment

Very high rates of change in temperature ( A T / A T ~107-109 Ks -I) occurring in the process of laser treatment of metal surface layers result in a change in the initial macrostructure of thus-fused metal layers [1-3]. The investigations carried out have proved that such a treatment can have a favourable effect on selected mechanical properties (e.g. microhardness) and electrical properties (e.g. resistance to electro-erosion in an electric arc) [1, 3]. It has also been found that in the newly formed layers of some metals considerable thermal stresses occur, which is evidenced by the presence of fractures in these areas of the fusion. This letter presents the results of microscopic examination of surface and metallographic cross-sections of tungsten, molybdenum and molybdenum with 1% silicon doping, subjected to laser treatment. The results of microhardness measurements performed by means of the Vickers method are also presented. In addition, selected results of the calculations of temperature fields and thermal stresses are given. The process of the local heating of the metal to temperature T < Tevaporating by the action of a single laser pulse on its surface and of the cooling (crystallization) of the fused area was analysed based on a model of a half-space heated with a surface, pulsed source of heat [1]. The results of the analysis have made it possible to determine intervals of the source power density and values of the heating time corresponding to these densities (Table I). An analysis of the cooling process shows that the rate of temperature change in the fusion, immediately after completion of the laser pulse, ranges from about 6 x 108 to 107 Ks -1 [1]. Such a high rate of cooling enables "freezing" of the dynamic state of the surface. This is confirmed by microscopic examination (Fig. 1) and literature reports [2]. Investigations of metallographic cross-sections of areas fused with laser radiation have revealed a change in the direction of arrangement of crystalline grains in relation to the initial fibrous structure (Fig. 1). Oblong grains occur here, oriented towards the point which, during the fusion, reaches the highest temperature.

Hardening treatment for the sliding supports of drill bits

TECHNOLOGY HARDENING TREATMENT FOR THE SLIDING SUPPORTS OF DRILL BITS O. V. Sizova, A. V. Kolubaev, V. I. Koveshnikov, G. V. Trusova, and S. Yu. Tarasov UDC 622.4.051 An increase in the driving rate and a reduction in expenditures for the drilling of wells in modern oil fields depend on the longevity and operating efficiency of the drill bits. The support is an important bit component, which determines the reliability of the structure on the whole. The most common problem in constructing the sliding supports consists in creating sur- faces of high hardness, which are uniform throughout the structure and which are formed from carburized and hardened steels [i] and composition anti-friction materials (for exam- ple, stellite) having a low coefficient of friction and high wear resistance [2]. Broad use of this type of hard-alloy materials as wear-resistant facings suppresses cracking of the facing layer, which significantly lowers the strength and fatigue properties of the sliding surface and is frequently the cause of so-called seizure due to separation of par- ticles in the failed layer. The firm Hughes Tool (United States) has adopted one of the recent technical solutions directed toward support surfaces with a high hardness. According to [3], the sliding sur- face of the bit journal is borided, as a result of which the strength and wear resistance of the support is increased by many times. This form of case hardening (CH) is not em- ployed in the domestic bit industry due to inadequate technical development of the method. We are proposing an original method for the complex boriding of the surface of a bit journal to replace the facing. The developed technology is a variety of CH and makes it possible to produce a wear-resistant layer of from 0.04 to 0.15 mm deep by the method of diffusion saturation with boron and other alloying elements. The studies were conducted on precarburized steel 15N3MA. Commercial boron carbide (GOST 5744-85) with a filler formed from aluminum oxides and other metals and commercial carbon was used as the boriding agent. The boriding was carried out over a period of 5 h0 After boriding, the specimens were subjected to hardening heat treatment. The phase com- position and thickness of the borided layer were determined by the metallographic method of "color etching" [4], from the results of microhardness measurements, and with the use of x-ray spectral analysis. The microstructure of the boride layers produced at different temperatures of the pro- cess is shown in Fig. i. The dark color belongs to the Fe2B phase, and the lighter color on the surface to the FeB phase. Attention is turned to the increase in the content of the FeB phase with increasing CH temperature. The maximum thickness of the FeB phase, as mea- sured over the ends of the boride needles, reached 60 ~m at a temperature of 940~ and the overall thickness of the dual-phase layer amounted to 160 ~m (see Fig. la). Only indi- vidual particles of the FeB phase are exposed at a treatment temperature of 920~ (see Fig. Ib), and iron monoboride is absent at 900~ (see Fig. le). The microhardness of the bo- rides under a loading of 1N amounted to H u = 19500-21500 MPa for the FeB, and H~ = 14000- 17000 MPa for the Fe2B. A characteristic feature of the boride layer produced at temperatures of 900 and 920~ is the "serration" of its structure, in the bed of whose roots a phase that cannot be tin- ted during color etching is present. This phase is manifested in the carburized layer as a result of the boron repelling the carbon back into the depths of the metal, and is, most likely, ultradisperse martensite. Its microhardness, as measured under a load of 1 N, is H u = 10000-11000 MPa. By varying the CH temperature, therefore, it is possible to obtain qualitatively dif- ferent structures of the boride coatings. The phase composition of the boride layer assumes Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 4, pp. 25-27, April, 19937 188 0009-2355/93/0304-0188512.50 9 1993 Plenum Publishing Corporation

Microhardness of the Surface Layer of Tungsten and Molybdenum After Recrystallization With Laser Radiation

We present results of microhardness measurements in melted local regions in molybdenum and tungsten. Microhardness has been measured by the Vickers method. Melted regions have been produced by pulsed Nd-glass laser. The emphasis is on correlation between conditions of recrystallization (energy of laser beam and method of irradiation-single pulse or multiple pulse) and the microhardness value.

Microhardness of flux grown pure doped and mixed rare earth aluminates and orthochromites

The results of microhardness measurements on flux-grown crystals of (i) single (pure) rare earth aluminates RAlO3 (R = Eu, Gd, Dy, Er) and rare earth orthochromites RCrO3 (R = Y, Gd, Yb), (ii) rare earth aluminates doped with neodymium, erbium, ytterbium and holmium, and (iii) mixed rare earth aluminate crystals of the type (La1−x) Pr(x)AlO3 (x=0, 0.25, 0.75 and 1.00) are presented. The variations in the microhardness value with load are non-linear in all cases. Kick's law fails to explain the observed variations. Instead, they are best explained by the application of the idea of materials resistance pressure in the modified law proposed by Hays and Kendall. The results indicate that the doping does not increase the hardness value of crystals in all cases. The hardness instead depends on the composition of the parent material as well as the dopant entering into the crystal lattice. Mixed rare earth aluminate crystals are shown to be harder than those of single rare earth aluminates.

Structural diagram of the TlSeDySe system

The structural diagram of the TlSeDySe system has been constructed by the methods of differential thermal analysis and the results of microhardness measurements. At room temperature the solubility of DySe is TlSe is established to be 4 mol%. As a consequence of the investigations, TlDySe 2 compound (paramagnetic) is disclosed at peritectic reaction.