Microhardness Of Specimens Research Articles

Experimental Study of Performance of Ti-6Al-4V Femoral Implants Using Selective Laser Melting (SLM) Methodology

Selective laser melting (SLM) technology used for the design and production of porous implants can successfully address the issues of stress shielding and aseptic loosening associated with the use of solid implants in the human body. In this paper, orthogonal experiments were used to optimize the process parameters for SLM molding of Ti-6Al-4V (TC4) material to investigate the effects of the process parameters on the densities, microscopic morphology, and roughness, and to determine the optimal process parameters using the roughness as a judging criterion. Based on the optimized process parameters, the mechanical properties of SLM-formed TC4 alloy specimens are investigated experimentally in this paper. The main conclusions are as follows: the optimal combination of roughness is obtained by polar analysis, the microhardness of SLM-molded TC4 alloy molded specimens is more uniform, the microhardness of specimens on the side and the front as well as the abrasion resistance is higher than that of casting specimens, the yield strength and tensile strength of specimens is higher than that of ASTM F136 standard and casting standard but the elongation is not as good as that of the standard, and the elasticity and compressive strength of porous specimens are higher than that of casting specimens at different volume fractions. The modulus of elasticity and compressive strength are within the range of human skeletal requirements. This work makes it possible to fabricate high-performance porous femoral joint implants from TC4 alloy SLM-molded materials.

Friction stir processing of AZ31 alloy to improve the mechanical, biodegradation, and in vitro biocompatible characteristics

The aim of the study was to improve the mechanical, biodegradation and in vitro biocompatible characteristics of as received rolled AZ31 (Mg-1%Zn-3%Al) alloy by develop the surface composite of Mg-Titania. The surface composite was developed by friction stir processing (FSP) and it’s used for prosthetic applications. The influence of tool rotation speed and number of FSP passes on grain structure, grain refinement, tensile strength, hardness, in vitro degradation rate and in vitro biocompatibility were explored. The obtained results support the capability of FSP in terms of mechanical strengthening, refinement of grain structure, dispersion of reinforcement (i.e. TiO2) and controlled degradation rate. Grain structure at stir zone, advancing side and retreating side were investigated. The large grains in the alloy were reduced to a fine equiaxial grains of average dimension of ≈ 3 μm by 3rd pass of FSP. The process was performed under two different tool rotation speed, i.e. 1550 and 2260 RPM. The addition of second phase in the matrix significantly improve the grain refinement. The results obtained from tensile test revealed the improvement in the percentage elongation without compromising the strength. The micro hardness of specimens of different parametric combination were evaluated and found ≈ 30–50% improvement in the micro hardness. The degradation rate by immersion test in simulated body fluid (SBF) for 3, 6 and 10 days were performed and found a significant reduction in degradation rate. The MTT assay for the biocompatibility performed by indirect method, the results validate the non-toxic behavior of processed specimen.

Effect of tool rotational speed on microstructure and mechanical properties of AA6061/SiC surface composites using friction stir processing

An investigation was conducted into how the tool rotation speed affected the microstructure and mechanical properties of friction stir processed samples based on AA6061-T6/SiC surface composites. The tool rotated between 700 and 1500 rpm with steps 400 rpm, while the other process variables were kept constant. Visual inspection reveals a sound and defect-free weld surface. The microstructure and particle dispersion of composite surface based on synthesis of aluminium alloys were revealed using an optical microscope. The findings demonstrate that rotational speed has a substantial impact on the uniform dispersion of SiC particles, which were observed at 1100 rpm found that refined and uniform distribution of particles as compared other rotational speeds. At tool rotational speed (TRS) of 1100 rpm, the friction stir processed specimen's microhardness and tensile strength, which seem to be 128 HV and 305 MPa, respectively.

Effect of different Cu6Sn5 morphology on the tribological properties of Babbitt alloy

PurposeThis paper aims to study different morphology Cu6Sn5 effect on Babbitt alloy tribological properties.Design/methodology/approachDifferent morphology Cu6Sn5 of Babbitt was conducted by different cooling modes. Bare Babbitt was marked by Babbitt-0, Babbitt modified by first cooling mode (marked by Babbitt-1) and Babbitt modified by second cooling mode (marked by Babbitt-2). The microstructure and microhardness of specimens were tested. Then, tribological properties of Babbitt-0, Babbitt-1 and Babbitt-2 were performed by reciprocating mode under lubricated condition.FindingsThe results showed that shape Cu6Sn5 of Babbitt was changed from mixed needle and star-like shape to short rod-like or granular shape. The microhardness of Babbitt-1 was highest than that of Babbitt-0 and Babbitt-2. Compared with Babbitt-0 and Babbitt-2, tribological properties of Babbitt-1 were better under lubricated condition due to short rod-like and sparse distribution of Cu6Sn5. Moreover, the simulation result of strain and stress of Babbitt-1 was lowest than that of Babbitt-0 and Babbitt-2.Originality/valueDifferent morphology (shape and distributed) of Cu6Sn5 was obtained by different cooling modes. Modulated different forms of Cu6Sn5 around SnSb was beneficial to improve Babbitt alloy tribological properties.

Effect of different disinfection protocols on the surface properties of CAD-CAM denture base materials

Statement of problemWhich disinfection protocol provides optimal water contact angle and microhardness for computer-aided design and computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA) materials is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of different disinfection protocols (1% sodium hypochlorite, denture cleanser gel, and effervescent tablet) on the water contact angle and microhardness of different CAD-CAM PMMA denture base materials by comparing them with a heat-polymerized PMMA. Material and methodsDisk-shaped specimens (Ø10×2 mm) were fabricated from 3 different CAD-CAM PMMAs—AvaDent (AV), Merz M-PM (M-PM), and Polident (Poli)—and a heat-polymerized PMMA (Vynacron) (CV) (n=21). Three disinfection protocols (1% sodium hypochlorite [HC], denture cleanser gel [GEL], an effervescent tablet [TAB]) were applied to simulate 180 days of cleansing. The water contact angle and microhardness of specimens were measured before and after disinfection and compared by using a 2-way ANOVA (α=.05). ResultsFor water contact angle, material (P=.010) and disinfection protocol (P=.002) had a significant effect. The material (P<.001), disinfection protocol (P=.001), and their interaction (P<.001) significantly affected the microhardness after disinfection. When the condition after disinfection was compared with that before disinfection, the water contact angle increased significantly in all material-disinfection protocol pairs (P≤.025), and microhardness increased significantly in all material-disinfection protocol pairs (P≤.040), except for GEL- (P=.689) or TAB-applied (P=.307) AV, HC-applied M-PM (P=.219), and TAB-applied Poli (P=.159). ConclusionsThe material and disinfection protocol affected the water contact angle of all tested PMMAs after disinfection, resulting in more hydrophobic surfaces for heat-polymerized or CAD-CAM PMMAs. The microhardness of heat-polymerized PMMA was less than that of all CAD-CAM PMMAs after disinfection, regardless of the protocol.

Defect Formation in Titanium Alloy during Non-stationary Process of Local Metallurgy

The paper studies Ti-6Al-4V alloy specimens obtained by wire-based electron-beam additive manufacturing (EBAM) and characterized by the structure with a defective region produced by uncontrolled wire fluctuations during 3D printing. Metallographic analysis and tensile strength tests and microhardness measurements are conducted to determine the defect influence on the structure and properties of the alloy. It is shown that the defective region represents the primary β-phase grains that are finer than those of the EBAM specimens commonly exhibiting a columnar structure. The specimen microhardness both in the defective and defect-free regions, is identical. The deformation behavior of the alloy is mostly subject to the influence of such defects, since the plasticity and ultimate tensile strength of the defective region are respectively higher and lower than that of the defect-free region.

An insight into microstructure and machining performance of deep cryogenically treated cemented carbide inserts

Abstract Cryogenic treatment is one of the potential techniques to enhance cutting tool performance. The present work investigates the microstructure and machining performance of cemented carbide (WC-Co) inserts through deep cryogenic treatment. For this, ISO P30 WC-Co inserts were exposed to deep cryogenic treatment (−196 °C), accompanied by tempering at 200 °C. The cryogenic treatment cycle helps to develop η (eta) phase carbides by redistributing cobalt (Co) phase on the surface of cryogenically treated WC-Co inserts. Microhardness of specimens indicated a slight increase in the hardness of cryogenically treated inserts than its untreated counterpart. A comparative performance evaluation between cryogenically treated tungsten carbide insert and the untreated insert was studied by turning of AISI 316 austenitic stainless steel through tool flank wear, crater wear, and chip morphology. Machining operation was carried out by considering three different cutting speeds (i.e. at 100, 150, and 200 m/min.) with constant feed rate and depth of cut of 0.2 mm/rev and 1 mm, respectively. After cryogenic treatment, significant improvement in the average flank wear and crater wear of WC-Co insert was observed. The enhancement of tool wear in the cryogenically treated insert is explained in detail by analyzing their microstructures.

Fracture behaviour of the 304 stainless steel with micro-EDMed micro-holes

Micro-electrical discharge machining (EDM) is an ideal technique for micro-hole drilling of 304 stainless steel. However, the local stress raiser at the holes and the concomitant microcracks generally leads to the strength degradation. In order to explore the appropriate approach of post-treatment to improve the degraded strength, a series of experiments were carried out to systematically understand the fracture behaviour of the 304 stainless steel with micro-EDMed micro-holes. In this study, array holes (3 × 3) with the diameter of 0.7 mm were fabricated by micro-EDM in the 304 stainless steel. The stress–strain curves and tensile fracture topography demonstrate that the fracture form of the micro-EDMed sample belongs to the combination of quasi-cleavage fracture and ductile fracture. By comparing the metallographic characterizations and the microhardness of specimens with and without micro-EDM, it is found that slippage occurs in the grains near the fracture of the micro-EDMed specimen and the elongation of grain is hardly observed. It is considered as the main reason that work hardening and grain refinement of the molten solidified layer formed during EDM limit the elongation of the surrounding grains.

Experimental study of factors affecting the failure of the cyclical nature of rotary endodontic instruments

Relevance. The properties of shape memory, superelasticity and plasticity in nickel-titanium tools make the visual prediction of breakage as difficult as possible. Therefore, an important role is given to research, the purpose of which is to predict the time of their work and to identify the main factors affecting the probability of a fracture.Aim. Comparison of cyclic fatigue resistance of Ni-Ti rotary endodontic instruments of various manufacturers.Materials and methods. The influence of the autoclaving procedure and the angle of bending of the root canal on the resistance of a rotating endodontic instrument to cyclic loads was studied using an author's patented device that simulates the rotation of an instrument in a real channel; the number of cycles completed by each instrument before its fracture was recorded. The morphology of fractures, the microstructure of specimens under fractures, and the microhardness of specimens of endodontic instruments after testing were studied.Results. It has been established that resistance to fatigue fractures of instruments of various endodontic systems decreases with an increase in the bending angle of the root canal. For Endostar E3 Basic Rotary System tools, the number of cycles decreased by 1.2 times, for Protaper Universal tools by 2.9 times. The tools of the Protaper Next system reduced the number of cycles at a bending angle of the artificial root canal of 60 degrees by 1.5 times compared with the number of cycles at a bending angle of 45 degrees. At the same time, statistical data and the study of the microstructure of samples of new and past 6 cycles of autoclave tools did not show a connection between the autoclaving procedure and a decrease in their resistance to cyclic loads.Conclusions. When working in complex bent over 45 degrees channels, it is rational to choose an endodontic instrument that has undergone heat treatment at the production stage (in the framework of this study, it was Protaper Next 25/06 M-Wire alloy). This will reduce the likelihood of a file fracture and associated dangerous complications of endodontic treatment.

Elastic and Mechanical Parameters of n-АМg6/С60 Nanocomposite under Cyclic Reversible Static Load

Results of experimental investigation into the effect of reversible mechanical loading–unloading on linear and nonlinear properties of n‑AMg6/C60 nanostructured composite are presented. For nanocomposite specimens, mechanical stress–strain curves are measured under many-cycle loading–unloading down to specimen fracture. The effect of cyclic loading–unloading on the microhardness of specimens is investigated. Within different characteristic portions of the stress–strain curve, nonlinear elastic properties of n-AMg6/C60 composite specimens subjected to several loading–unloading cycles are studied by Thurston–Brugger and spectral methods. The results of experimental studies are discussed.

The Influence of Duration of Preliminary Mechanical Activation on Microhardness of Specimens of Ni3Al Intermetallide Synthesized Under Conditions of Spark Plasma Sintering

The Influence of Duration of Preliminary Mechanical Activation on Microhardness of Specimens of Ni3Al Intermetallide Synthesized Under Conditions of Spark Plasma Sintering

Effects of fluoride versus amorphous calcium phosphate solutions on enamel microhardness of white spot lesions: An in-vitro study.

BackgroundDevelopment of white spot lesions around orthodontic fixed orthodontic appliances is a common finding, especially in patients with poor oral hygiene. One of the conservative interventions for regression of these lesions is using chemical solutions. The current study aimed to compare the effectiveness of fluoride and amorphous calcium phosphate (ACP) on microhardness improvement of affected enamel.Material and MethodsForty-five intact human incisor teeth were selected and randomly divided into 3 groups of 15. Fluoride group, ACP group and artificial saliva group (control group). Inducing of white spot lesion was done by PH-cycling model. Samples of the first and second group were submerged into 0.05% fluoride and 0.05% ACP solutions respectively for one minute a day. The rest of the time, all specimens were put in artificial saliva, which was incubated in 37 °c temperature. Microhardness of specimens was assessed by Vickers microhardness test in three stages: 1: Baseline microhardness assessment that was done before induction of white spot lesion, 2: Secondary microhardness assessment that was done after induction, 3: Final microhardness assessment that was done after chemical treatment. The SPSS 11.5 software was used for statistical analysis and p< 0.05 was considered as significant.ResultsMicrohardness of specimens in the fluoride and ACP groups had significantly improved after the treatment (between secondary assessment and final assessment). In the control group, no significant improvements were observed. In final assessment, there were significant differences between the ACP and control groups, but no significant differences were found neither between the fluoride and ACP, nor the Fluoride and control groups.ConclusionsAccording to the current study, both 0.05% ACP and 0.05% fluoride solutions enhanced enamel micro-hardness in treatment of white spot lesion. Key words:Microhardness, amorphous calcium phosphate, fluoride, white spot lesion.

Effect of ambient pH and different chewing cycle of contact wear on dental composite material

Background: The purpose of this study was to effect of ambient pH and different two chewing cycles of wear on restorative nanohybrid- and microhybrid-filled composite material in intraoral tribology. Methods: All specimens were stored in the artificial saliva for 7 days before the chewing tests. Then, composite specimens were subjected to chewing simulation using a computer-controlled chewing simulator (F = 50N [vertical movement 2 mm and horizontal movement 0.7 mm] 120.000 and 240.000 chewing cycles, 1.2 Hz frequency, and 37°C ambient temperature), immersed artificial saliva (about pH = 5.7), and citric acid solution (about pH = 3.2). Steatite balls were used as antagonists for every experiment chewing test cycle (d = 6 mm). Specimen's microhardness values determined with Vickers hardness method before chewing tests. Mean volume loss values were determined using noncontact three-dimensional (3D) laser scanning device. Furthermore, two-dimensional and 3D analysis of the mean volume loss wear surface of the composite material was performed both immersed artificial saliva and citric acid. Mean values and standard deviations were calculated and statistical analysis was performed using one-way analysis of variance. In addition, scanning electron microscopy analysis was performed to examine surface wear tracks. Results: The surface morphology of both composite materials was severely damaged in immersed citric acid solution. This can be explained by the more damage to the organic matrix structure of the composite material in citric acid solution than immersed artificial saliva. Conclusion: The results obtained in this study will help to understand the effect of the pH value of the third abrasive surface on the composite material in the three-body wear mechanism.

Effect of Hygrothermal Loading on Laminate Composites

Objective: To find the effect of hygrothermal loading on CFRP and GFRP composite materials by finding the properties like capacitance, micro hardness, moisture diffusivity and area of fraction. Methods: Hand layup and vacuum bag methods were used for fabrication of composites. Finding: Three-point bending test was done on each specimen by varying load, i. e, zero load, with 30% load, 50% load and 70% load for different time periods. Micro hardness and capacitance were determined using Vickers Hardness tester and LCR meter respectively on both the composites before and after the thermal treatment. The capacitance increased with time whereas the percentage area of fraction of the fibre decreased. Also, the reduction in strength and damage to fibre were investigated using SEM. It was observed that with increase in %weight gain, micro hardness of specimen decreased. Application/Improvement: FRPs can substitute traditional steel reinforcements in reinforced concrete structures. The continuous loading under thermal actions due to natural environmental factors lead to degrading effect that needs to accurate investigations in evaluating durability of fibre reinforced polymers.

Investigating the effects of traveling speeds and post-weld heat treatment on mechanical properties of nano-Al2O3-fortified AA6061-T6 friction stir welds

In this study, 6 mm thick AA6061-T6 plates were friction stir welded (FSWed) at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. The solution heat treatment was applied on samples for one hour at 540 ℃ and subsequently aged for 18 h at 180 ℃ to investigate the effect of post-weld heat treatment on mechanical properties of specimens. All joints were investigated macro- and micro-structurally. The microstructural characterization of the FSWed samples was carried out using scanning electron microscopy (SEM) and light microscopy techniques. Distribution of Al2O3 nano-particles in the stir zone was studied by SEM. The specimen FSWed at 40 mm/min exhibited the most homogeneous particles distribution. Tensile properties including ultimate tensile strength, elongation, and fracture surfaces were studied. Microhardness of specimens was also investigated. Surprisingly, all specimens exhibited inferior hardness compared to the as-received AA6061-T6 alloy. This phenomenon was attributed to the dissolution of precipitates during FSW process.

A Study on Effect of Beginning V Concentration in TD Process

Procedures of thermal diffusion (TD) process are carried out on two specimens of Cr12MoV steel using the same salt bath formula. For the two specimens, the beginning V concentration, V concentration at the time specimen is added, are different, the level of which is controled by changing the interval between the specimen are added and the time reducing agent of Al meeting with vanadizing source of V2O5. The interval for Specimen 1 and Specimen 2 are 10 and 30 minutes respectively. Consequently, different changes are happened on the surface of the substrates. The microstructures of coatings are observed by optical metallographic microscope and SEM/EDS, the hardness are tested by Vickers micro-hardness tester. Results show that: VC coating formed on Specimen 2 is of better performances than Specimen 1, microhardness of Specimen 2 reaches as much as 2400HV. It can be concluded that level of V concentration at the beginning of TD process is a vital factor for the forming of VC layer.

Nd:YAG Laser Irradiation of the Tooth Root Surface Inhibits Demineralization and Root Surface Softening Caused by Minocycline Application

The aim of this study was to investigate the effect of laser irradiation on root surface demineralization caused by local drug delivery systems (DDS), and to evaluate the effect of sealing on drug retention. The duration of supportive periodontal treatment (SPT) has increased with increasing life expectancy. Repeated root planing and DDS application during SPT should be reconsidered with regard to their effects on the root surface. Extracted human teeth were collected, cut into 3 × 3 × 2 mm root dentin specimens, and divided randomly into eight groups with various combinations of Nd:YAG laser power (0, 0.5, 1, and 2 W), with and without DDS (minocycline HCl). Specimen microhardness and calcium (Ca) solubility were measured after treatment. The specimens (control and laser and DDS groups) were examined by scanning electron microscopy. Forty SPT patients were recruited, to assess the effect of periodontal pocket sealing on drug retention. Laser irradiation increased the microhardness of root specimens in an energy-dependent manner. Calcium solubilities decreased from the 0 W+DDS group to the 2.0 W+DDS group. The mean Ca solubilities in the 1.0 W+DDS and 2.0 W+DDS groups were significantly lower than in the 0 W+DDS group (p<0.01, p<0.001, respectively). Laser irradiation counteracted the softening effect of DDS. Morphologic change was observed in the 2 W+DDS group; however, no morphologic changes were observed in the control and the 1 W+DDS groups. The mean concentration of minocycline in the periodontal pocket 24 h after application was 252.79 ± 67.50 μg/mL. Laser irradiation of the root surface inhibited the softening and decalcification caused by minocycline HCl. Sealing the periodontal pockets effectively improved drug retention. These results suggest that the combination of laser irradiation and DDS could benefit patients receiving repeated SPT.

Characterization of electrodeposited Ni–SiC–Cg nanocomposite coating

Nickel–silicon carbide–graphite (Ni–SiC–Cg) nanocomposite coating was deposited onto the steel (St-37) substrate by electrochemical plating method. The influence of pH parameter on the mechanical properties and morphological features was studied. The coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Elemental mapping analysis system, and field emission scanning electron microscopy (FE-SEM) techniques. Besides, the microhardness of specimens was measured by Micro hardness Tester. Based on XRD results, the dominant phases with high crystallinity degree were nickel, silicon carbide and graphite. Microscopic observations illustrated that all the coatings had a cluster like structures which consisted of some fine sphere particles with an average crystallites size of 60nm. Among of all coatings, the specimen at pH equal to 4.8 presented an appropriate morphology as well as lower porosity with high grain boundaries. Moreover, elemental mapping spectra exhibited a homogenous distribution of nickel, silicon and carbon particles. However, the distribution of silicon particles into nickel matrix at pH=4.8 was higher than the other samples. Also, mechanical properties of the attained coatings were improved with increasing of pH values up to 4.8 (593 HV) which is in agreement with microstructural characteristics. Therefore, obtaining of the optimum pH value is the major parameter in electroplating of Ni based nanocomposite which affected microhardness and distribution of reinforcement particles into the matrix.

Mechanical properties and microstructural evolution during multi-pass ECAR of Al 1100–O alloy

The main objective of this work is to achieve ultra-fine grained structures within the pure aluminum sheet via equal channel angular rolling (ECAR). An attempt has been made to investigate the microstructural evolution and mechanical properties of the processed specimens in terms of process pass numbers and routes. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) examination showed ultra-fine grains (UFGs) with the average grain size of 0.85, 0.34μm for the seventh pass, respectively. Yield and tensile strengths and microhardness of specimens were significantly increased upon the first pass; however, elongation was dramatically reduced. Subsequent process cycles caused no considerable improvement on the mechanical properties.

Development of a Non-Contact Micro-Deburring Method Using Ultrasonic Cavitation Bubbles

The purpose of this study is to develop a non-contact deburring method and optimize its operation parameters. A deburring method using enhanced ultrasonic cavitation without abrasives is proposed and its work conditions were optimized. In additional, aging changes on the microhardness and surface roughness of specimens were studied experimentally in the process. The aging microhardness went through two stages. In the first stage, the work hardening characteristic of aluminum induced the increase in microhardness of specimen. After the microhardness reached an extreme, it went down. The surface roughness increased with treatment time. These time-dependent changes indicated that parts should be treated discontinuously during the ultrasonic deburring process to avoid being eroded by cavitation bubbles. Deburring experiments indicated that the burrs can be effectively removed by these enhanced cavitation bubbles.