Decrease In Microhardness Research Articles

Surface integrity of quenched steel 1045 machined by CBN grinding wheel and SiC grinding wheel

PurposeThe purpose of this paper is to evaluate surface integrity of quenched steel 1045 ground drily by the brazed cubic boron nitride (CBN) grinding wheel and the black SiC wheel, respectively. Surface integrity, including surface roughness, sub-surface hardness, residual stresses and surface morphology, was investigated in detail, and the surface quality of samples ground by two grinding wheels was compared.Design/methodology/approachIn the present work, surface integrity of quenched steel 1045 machined by the CBN grinding wheel and the SiC wheel was investigated systematically. All the specimens were machined with a single pass in the down-cutting mode of dry condition. Surface morphology of the ground specimen was observed by using OLYMPUS BX51M optical microscopy. Surface roughness of seven points was measured by using a surface roughness tester at a cut-off length of 1.8 mm and the measurement traces were perpendicular to the grinding direction. Sub-surface micro-hardness was measured by using HVS-1000 digital micro-hardness tester after the cross-section surface was polished. The residual stress was tested by using X-350A X-ray stress analyzer.FindingsWhen the cut depth is increased from 0.01 to 0.07 mm, the steel surface machined by the CBN wheel remains clear grinding mark, lower roughness, higher micro-hardness and higher magnitude of compressive stress and fine microstructure, while the surface machined by the SiC grinding wheel becomes worse with increasing of cut depth. The value of micro-hardness decreases, and the surface roughness increases, and the surface compressive stress turns into tensile stress. Some micro-cracks and voids occur when the sample is processed by the SiC grinding wheel with cut depth 0.07 mm.Originality/valueIn this paper, the specimens of quenched steel 1045 were machined by the CBN grinding wheel and the SiC wheel with various cutting depths. The processing quality resulted from the CBN grinding wheel is better than that resulted from the SiC grinding wheel.

Microstructure Evolution and Biodegradation Behavior of Laser Rapid Solidified Mg–Al–Zn Alloy

The too fast degradation of magnesium (Mg) alloys is a major impediment hindering their orthopedic application, despite their superior mechanical properties and favorable biocompatibility. In this study, the degradation resistance of AZ61 (Al 6 wt. %, Zn 1 wt. %, remaining Mg) was enhanced by rapid solidification via selective laser melting (SLM). The results indicated that an increase of the laser power was beneficial for enhancing degradation resistance and microhardness due to the increase of relative density and formation of uniformed equiaxed grains. However, too high a laser power led to the increase of mass loss and decrease of microhardness due to coarsened equiaxed grains and a reduced solid solution of Al in the Mg matrix. In addition, immersion tests showed that the apatite increased with the increase of immersion time, which indicated that SLMed AZ61 possessed good bioactivity.

Novel compositions of Bi2O3-ZnO-TeO2 glasses: Structure and hardness analysis

Tellurite based glasses have been prepared with various glass compositions such as yBi2O3-xZnO-(100−x−y)TeO2 glass system (y=0.2, 1.0, 2.0, 3.0, 4.0, 5.0, and 8.0mol% ratio and x=14, 19, 19.8, and 20mol%). The purpose of the work is to investigate the effect of glass compositions on the structure and hardness under the indentation loading test. Up till now, the experiences of the preparation of tellurite based glasses showed that it has high fragility structure at room temperature compared to boroxide, and chalcogenide-based glass materials. In this study, the thermal, mechanical and structural properties of Bi - based tellurite optical glass materials were investigated at room temperature. Results indicated that increased refractive index ratio of Bi has pronounce effect upon the transition temperature while the hardness value of the lassy material showed a reduction in response to this increased refractive index value of Bi. The obtained results further could be correlated with compositions that effects on the structural changes [for TeO4 (tbp) to TeO3 (tb)] having non-binding oxygen (NBO) due to the elastic deformation of TeO bonding and expansion of interatomic distances when considered the data of the Vickers' hardness, FT-IR, and Raman spectra. Here, it can also be emphasized that obtained the thermal stability, (T=Tx−Tg), of the glass material, decreases from 80 to 37°C as the melting temperature increases from 800 to 1025°C, possibly leading to a decrease in microhardness and deformation in the glass materials.

Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of AlSiTi phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Resistance spot welding of ultrafine grained/nanostructured Al 6061 alloy produced by cryorolling process and evaluation of weldment properties

Resistance spot welding process was used to produce ultrafine grained/nanostructured Al 6061 alloy joints. In this regard, ultrafine grained/nanostructured 6061 aluminum sheets were first produced by cryorolling and then joined by resistance spot welding. For this purpose, the samples were solution treated at 530°C for 3h and subsequently cryorolled up to 90% reduction in thickness. In order to improve strength and ductility, the cryorolled sheets were then subjected to ageing treatment. The average size of fine grains of the peak aged alloy reached to ∼60nm. In peak aged condition, an ultimate tensile strength of 365MPa, a hardness of ∼140HV and a ductility of 11.8% was obtained. The cryorolled, peak aged, and also 6061-T6 Al alloy sheets (witness samples) were then resistance spot welded. Results showed that the cryorolling process can effectively increase the electrical resistivity of Al 6061 alloy. From tensile-shear tests, the highest peak load of spot welds was obtained for the cryorolled specimens. This is due to higher electrical resistivity of the cryorolled samples which increases the nugget diameter and therefore the peak load of the spot welds. A decrease in microhardness was observed in the fusion zone due to dissolution of Mg2Si strengthening precipitates in this region during welding process.

Microstructure and thermal fatigue resistance of Co-based alloy coating on H13 steel by laser cladding

Thermal fatigue failure is easy to occur on H13 steel surface under working condition, the Co-based coating was fabricated by Nd:YAG laser on H13 steel. Microstructure, distribution of elements and composition of phases were investigated by means of optical microscope(OM), scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and X-ray diffraction(XRD).The effect of thermal fatigue on microhardness of Co-based coating and quenching-tempering H13 steel was tested by microhardness tester. The results show that: From bottom to the surface of Co-based coating, planar crystal, cellular crystal, dendrite crystal and equiaxed crystal were observed; Co-based alloy coating is mainly composed of -Co and M23C6, M2O3 and M3O4(M=Fe, Co, Cr)are produced on the surface of coating after thermal cycling; Microhardness of Co-based coating which could reach 706HV0.2, decreased gradually. After 1000 thermal cycles, the microhardness decreases of Co-based alloy coating and H13 steel are 24.4% and 37.7%, respectively; The surface of the Co-based coating has no thermal cracks, while that of H13 steel has a large number of thermal cracks; Cr2O3 oxide film is formed on Co-based alloy coating, which makes thermal fatigue resistance of coating better than that of H13 steel.

THE EFFECT OF CHITOSAN AND PROPOLIS IRRIGATION ON ROOT DENTIN MICROHARDNESS

Introduction: The aim of the present study is to evaluate comparatively the action of 0.2% chitosan, 4% propolis, 2.6 % NaOCl and 17% EDTA on human root dentin microhardness. Methods: Twenty recently extracted single-rooted mandibular premolar teeth were selected. The roots were split longitudinally into 2 parts (40 specimens). The specimens were randomly divided into 4 groups and were treated with 0.2% chitosan, 4% propolis, 2.6 % NaOCl and 17% EDTA immediately after the initial baseline microhardness measurements. A standardized volume of 2 ml of each solution was used for 5 minutes. The reference microhardness values of untreated specimens were initially measured with a Vickers indenter under a 50-g load and a 10-second dwell time. Posttreatment microhardness values were obtained in the same manner as the initial ones. The decrease in microhardness was calculated as a percentage. Data were analyzed statistically by 1-way analysis of variance (P = .05) and the post hoc Tukey test for multiple comparisons at the same level of significance. Differences between pretreatment and post-treatment microhardness were statistically analyzed by using the t-test with a P value of .05 Results: After treatment, all solutions significantly decreased the microhardness of root dentin (P < .05) however both 0.2% chitosan, 4% propolis significantly decreased dentin microhardness compared to 2.6 % NaOCl and 17% EDTA. Conclusion: All the tested irrigation decreased root dentin microhardness however the effect of either 0.2% chitosan or 4% propolis decreased root dentin microhardness more than 2.6% NaOCl or 17% EDTA.

Упрочнение конструкционной стали с помощью многоканального СО2 лазера

Studies are carried out on the microstructure and micro-hardness distribution of structural steel 30HN3А samples hardened by laser quenching by means of continuous radiation from a multi-channel 48 rays CO2 laser system CLT-Yu-5. To provide the formation of a uniform structure, hardness and depth distribution in the hardened material layer a laser emitter was used with four plug-in radiating tubes arranged one into another in an octahedral configuration (patent RF № 2580350). An important role of a high uniformity of the integral heat input across the hardening zone width on the uniformity of properties of the hardened layer is demonstrated. It was found that in the hardened area a finely dispersed martensite structure was formed. The carbides contained in the initial structure of sorbite dissolve not completely during laser hardening. They are characterized by a globular form and size of 0.2...0.3 µm. The microhardness of steel in the hardened area was about 6800 MPa. The thickness variation of the hardened layer, which is characterized by the ratio between minimal, hmin, and maximal, hmax, depths, is equal to 0.76 at hmax = 1050 µm. A reduction in microhardness in a tempering zone formed between two successive hardened bands down to the values of 5500...6000 MPa was found. The width of this tempering zone is about 1.8 mm. The decrease of microhardness in this zone is due to a dissociation of the martensite and formation of tempering troostite structure. Lamellar carbides are formed during this process. Steel in the laser hardened area has a favorable structure in terms of the strength and durability. Thus, hardening of steel by means of multi-channel CO2 laser systems provides wide opportunities in improving of material properties and is recommended for hardening of expensive machine parts increasing their service lifetime.

Comparative evaluation of Nano-Hydroxyapatite preparation and Calcium Sucrose Phosphate on microhardness of deciduous teeth after iron drop exposure - An in-vitro study.

BackgroundTo evaluate and compare the microhardness of deciduous teeth treated with nano-hydroxyapatite and calcium sucrose phosphate after iron drop exposure.Material and MethodsTwenty healthy anterior deciduous teeth were collected and stored in 0.9% saline solution at room temperature. All the teeth were immersed in artificial saliva in an incubator shaker at 37° for an hour and then subjected to Vickers microhardness test at 100g load for 5 seconds. The teeth were then immersed in iron drop for 5 minutes, twice daily, rinsed with distilled water and kept in artificial saliva. This procedure was repeated for 7 days and teeth were subjected to microhardness testing. Further, the teeth were divided in two groups, each group containing 10 teeth. In group I, nanohydroxyapatite preparation and in group II, calcium sucrose phosphate were applied for 10 minutes, twice daily for 7 days and subjected again to microhardness testing again.ResultsVickers microhardness analysis revealed that iron drop exposure to teeth caused significant decrease in microhardness (p<0.05). Application of nanohydroxyapatite preparation in Group I showed significantly increased enamel microhardness (206.90) than that after iron drop exposure. Similarly, application of calcium sucrose phosphate in Group II showed significantly increased enamel microhardness (200.89) than that after iron drop exposure. Statistical difference was seen between the two groups, with nanohydroxyapatite preparation showing increased microhardness than calcium sucrose phosphate.ConclusionsNanohydroxyapatite preparation and calcium sucrose phosphate have remineralizing effect over teeth affected by acid challenge of iron drops, nanohydroxyapatite preparation showing better results than calcium sucrose phosphate. Key words:Iron drops, Nanohydroxyapaptite, calcium sucrose phosphate, anticay.

Effect of two different tooth bleaching techniques on microhardness of giomer.

BackgroundTooth bleaching is a safe and conservative treatment modality to improve the esthetic appearance of discolored teeth. One of the problems with the use of bleaching agents is their possible effect on surface microhardness of resin-based materials. The present study was carried out to evaluate the effect of in-office and at-home bleaching on surface microhardness of giomer.Material and MethodsSeventy-five disk-shaped giomer samples (Beautifil II) were prepared and cured with a light-curing unit. The samples were randomly assigned to three groups (n=25). In group 1 (control), the samples were stored in distilled water for 14 days. The samples in groups 2 and 3 underwent a bleaching procedure with 15% carbamide peroxide (CP) (8 hours daily) and 45% CP (30 minutes daily), respectively, for 14 days. Finally, the microhardness of samples was measured with Vickers hardness tester using a 100-g force for 20 seconds. One-way ANOVA was used to compare the mean microhardness values among the study groups, followed by post hoc Tukey test for two-by-two comparison of the groups. Statistical significance was set at P<0.05.ResultsOne-way ANOVA showed significant differences in the mean microhardness values among the study groups (P<0.001). Based on the results of Tukey test, microhardness in the bleached groups was significantly less than that in the control group (P<0.0005). In addition, microhardness in the 45% CP group was significantly less than that in the 15% CP group (P<0.0005).ConclusionsUse of both bleaching agents during in-office and at-home bleaching techniques resulted in a decrease in surface microhardness of giomer. The unfavorable effect of in-office bleaching (45% CP) was greater than that of at-home bleaching (15% CP). Key words:Dental restorations, hardness, tooth bleaching.

An experimental study of exploitation of materials used for prosthetic temporary restorations

Temporary restorations more often play their role for a definitely longer period of time, than the time necessary for implementation of final prosthetic work. Therefore, they are subjected to adverse effects of chemical, physical and thermal factors in a patient's oral cavity. Since loss of temporary prosthetic work can have negative consequences for an entire treatment process, it is important to identify a potential risk of damaging temporary restorations by factors derived from the diet of patients. The aim of this study was to evaluate the influence of components of the beverages, such as coffee and tea, consumed daily by the patients, on the mechanical properties of materials used in temporary restorations. The experimental design applied, as well as gained results, were justified by appropriate, chosen statistical methods. The conducted research demonstrated the change of mechanical properties of studied materials for their flexural strength, as well as microhardness. The tendency of changes in both result variables, compared with the samples kept in neutral environment – distilled water, indicates the decrease in mechanical strength and microhardness of materials conditioned in coffee and tea. It can be claimed that the components of beverages present in an everyday diet of patients have a considerably adverse effect on the quality of materials used for provisional crowns and bridges.

Effect of sintering parameters on densification, corrosion and wear behaviour of Ni-50Fe alloy prepared by spark plasma sintering

Spark plasma sintering (SPS) technique was used to fabricate Ni50Fe alloys. Powders were sintered at various temperatures, pressure and holding times ranging between 900 and 1100 °C, 40–50 MPa and 5–10 min respectively. Microstructural characterisation was carried out using scanning electron microscopy (SEM). Archimedes' method for density measurements, vickers microhardness, and tribometer were used to study the effect of various sintering parameters on the densification, electrochemical properties in 1 M H2SO4 solution, coefficient of friction (CoF) and dry sliding wear resistance. An increase in sintering temperature was found to enhance densification and the highest density was reported at 1100 °C sintered for 10 min with 50 MPa, with a slight decrease in microhardness. Increasing temperature was also found to be reducing corrosion resistance but improving alloy wear resistance against the tungsten carbide counter body. The effect of sintering time and pressure was found to be of minor effect on both corrosion and wear resistance. Fractography studies indicated the dominant fracture micromechanism as ductile fracture of sintering necks. The main wear mechanism of Ni-50Fe alloy was attributed to the simultaneous actions of ductile and brittle friction mechanism with the existence of abrasion and delamination of worn surfaces.

Texture and microstructure evolution of Incoloy 800H superalloy during hot rolling and solution treatment

In this paper, we have implemented a specific hot rolling and solution treatments on Incoloy 800H to examine the evolution of texture and microstructure during this process. We also focused on the analysis of local misorientation (LM) and grain boundary character distribution through electron backscattered diffraction (EBSD) method. The results showed that the hot-rolled microstructure is mainly composed of elongated grains with typical texture components of B, Cu and S at the mid-layer of plates, while substantial inhomogeneous fine grains can be observed between the deformation grains at the surface-layer showing a combination of R-C and R-Cu components. Following solution treatment, the original deformed grains are fully substituted by the fine recrystallized grains and the grain size increases significantly at higher solution temperatures. An alternant lamellar structure of fine and coarse grains forms along the rolling direction at 1050 °C due to the pinning effect of TiC at fine grains boundaries. Besides, C and G are the dominant texture components after solution treatment. With increasing solution temperature, the overall level of LM and micro-hardness decrease stably and a higher ratio of Σ3:Σ(9 + 27) indicates that Σ3n boundaries proliferation mechanism transforms from “Σ3 regeneration” to “new twinning”.

Effect of Coating Removal by Induction Heating on the Microstructure and Properties of Deck Steel

Deck steel with anti-skid coating is treated by induction heating for coating removal. The microstructure of cross-section before and after coating removal is observed by metallographic microscope and scanning electron microscope. Z-direction micro-hardness of cross-section before and after coating removal is tested by micro-hardness tester. Results show that the softening layer of about 3 mm, which the average micro-hardness of the layer is 244 HV, is formed on the surface of the sample. The micro-hardness decreases by 3.5% compared with the untreated sample. Coating removal by induction heating will not have an impact on the metallographic structure. But carbide particles will be precipitated at the grain boundary. At last, the influence of induction heating on the performance of deck steel is briefly analyzed.

Influence of Co0.5Zn0.5Fe2O4 Nanoparticles Addition on Vickers Microhardness for Cu0.5Tl0.5-1223 Phase

(Co0.5Zn0.5Fe2O4) x /Cu0.5Tl0.5Ba2Ca2Cu3O10−δ samples, 0.00 ≤x≤ 0.20 wt%, were synthesized using a one-step solid-state reaction technique. Co0.5Zn0.5Fe2O4 nanoparticles were examined using X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). All prepared samples were characterized using XRD, scanning electron microscopy, (SEM) and electrical resistivity measurements. Vickers microhardness measurement for (Co0.5Zn0.5Fe2O4) x /Cu0.5Tl0.5Ba2Ca2Cu3O10−δ samples was carried out at room temperature under different applied loads varying from 1 to 10 N. Vickers microhardness (H V) increases as x increases up to 0.08 wt%, and then it decreases with further increase in x. In addition, Vickers microhardness shows its dependence on the holding time of the indenter under applying constant loads. All samples exhibit indentation size effect (ISE) with normal trend, as Vickers microhardness decreases by increasing the applied loads. Different models were used to analyze the obtained results such as Meyer’s law, Hays–Kendall (HK) approach, elastic/plastic deformation (EPD) model, proportional specimen resistance (PSR) model, and modified proportional specimen resistance (MPSR) model. The experimental results of Vickers microhardness are well fitted according to the MPSR model. Some important mechanical parameters such as Young’s modulus (E), yield strength (Y), fracture toughness (K f), and brittleness index (B i ) were calculated as a function of Co0.5Zn0.5Fe2O4 nanoparticle addition. These parameters depend on the weight percent addition of Co0.5Zn0.5Fe2O4 nanoparticles into Cu0.5Tl0.5-1223 phase.

Change of deformation characteristics and dislocation substructure of nonferrous metals under influence of magnetic field

The objects of the study were polycrystalline copper of M00b grade and commercially pure titanium BT1-0. Microindentation was carried out on the samples of titanium BT1-0 in the initial state, immediately after magnetic field exposure of 0.4 T and after certain time intervals. The defect substructure of cooper samples M00b, subjected to loading to failure in the creep mode under the influence of magnetic field of 0.35 T and without it, was investigated by the methods of electron diffraction microscopy. It was revealed that the effect of magnetic field exposure on commercially pure titanium BT1-0 leads to the decrease in microhardness with the subsequent stabilization during the time that depends on the processing parameters. And the effect of the magnetic field exposure on copper during the process of creeping results in the redistribution of dislocation substructure types. Also, there are changes in quantitative characteristics of dislocation substructures.

Preparation and characterization of porous hydroxyapatite pellets: Effects of calcination and sintering on the porous structure and mechanical properties

In this study, porous hydroxyapatite structures were produced by using urea particles of 600–850 µm size. Samples with two different urea composition (25 and 50 wt%) were prepared along with samples without any urea content by adding urea to commercially available hydroxyapatite in its as purchased and calcined states. The produced pellets were sintered at 1100 ℃ and 1200 ℃ for 2 h. Compression tests and microhardness measurements were conducted and changes in density values were examined in order to determine the effect of the calcination state of the prior hydroxyapatite powder, the sintering temperature and the amount of urea added. Also X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analyses were conducted to determine the phase stability, functional groups, and pore morphology, respectively. Calcination is found to negatively affect the densification and sinterability of the produced samples, resulting in a decrease of compressive strength and microhardness. With the control of the urea content and sintering temperature uncalcined hydroxyapatite can successfully be used to tailor the density and mechanical properties of the final porous structures.

Role of PEO coatings in long-term biodegradation of a Mg alloy

Long-term effect of plasma electrolytic oxidation (PEO) coatings on in vitro corrosion of 3D Mg implant specimens has been investigated in simulated body fluid (SBF). Hydrogen evolution rate in PEO-coated specimens was 35 times lower compared to the non-coated alloy during first 2 weeks of immersion (0.04–0.07mLcm−2d−1) and reached a steady-state rate of 0.3mLcm−2d−1 by week 6 of immersion. Studies of the tribocorrosion behaviour of the PEO-coated alloy disclosed that the coatings rapidly lose their tribocorrosion resistance due to hydration of the coating material and associated drastic decrease of microhardness but exhibit a better tirbocorrosion performance than the non-coated material.

Surface modification by electrolytic plasma processing for high Nb-TiAl alloys

Metal surface modification by electrolytic plasma processing (EPP) is an innovative treatment widely commonly applied to material processing and pretreatment process of coating and galvanization. EPP involves complex processes and a great deal of parameters, such as preset voltage, current, solution temperature and processing time. Several characterization methods are presented in this paper for evaluating the micro-structure surfaces of Ti45Al8Nb alloys: SEM, EDS, XRD and 3D topography. The results showed that the oxide scale and other contaminants on the surface of Ti45Al8Nb alloys can be effectively removed via EPP. The typical micro-crater structure of the surface of Ti45Al8Nb alloys were observed by 3D topography after EPP to find that the mean diameter of the surface structure and roughness value can be effectively controlled by altering the processing parameters. The mechanical properties of the surface according to nanomechanical probe testing exhibited slight decrease in microhardness and elastic modulus after EPP, but a dramatic increase in surface roughness, which is beneficial for further processing or coating.

Effect of Gamma Radiation on Mechanical Properties of Tooth Structure

This in vitro study was made to evaluate the effect of gamma radiation on mechanical properties of tooth structure. A total number of 40 human premolar teeth were collected. The teeth were healthy and were freshly extracted and they were stored in distilled water for periods of less than one month the teeth were, free from any apparent caries,macroscopic cracks, and abrasion and staining as assessed by visual examination.The teeth were divided into 2 groups of 20 teeth each (A and B) The groups were: 1. Group (A) which served as a control.2. Group (B) which subjected to 60 Gy of γ- radiation. The result showed the enamel microhardness increased after adose of 60 under the limitation of this study it was found that. The enamel microhardness increased at a dose of 60GY whereas the value of dentin microhardness decreases.