Cross-sectional Hardness Research Articles

Prediction of microstructure and mechanical properties of line pipe welded joints based on hardness map

In this article, the variation of hardness in cross-section of X52 microalloyed steel joints before and after post-weld heat treatment and also the relationship of hardness with ultimate tensile strength, yield strength and microstructure have been investigated. For this purpose, the specimens were prepared in two conditions of as welded and post-weld heat treated, and the hardness maps of their cross-section were provided. Then, some equations were suggested to correlate the obtained hardness with the grain size and tensile and yield strengths. The equations made it possible to predict tensile and yield strengths with high accuracy. According to the results, the maximum hardness and strength belong to the weld junction. Normalisation of the joints at 950°C reduced significantly the hardness difference (and also the strength difference) in various joint areas and homogenised the microstructure considerably. The grain size distribution was also modelled acceptably for the post-weld heat treated joint, and the grain size map was obtained.

RESULTS OF THE USE OF IMPORT RAILS IN THE EAST SIBERIAN RAILWAY

Metallographic examination of a rail of R65 type produced in Japan has been conducted after its use in the East-Siberian Railway has been conducted. It has been shown that, as for the chemical composition, the metal sample meets the requirements of the specifications of TU 0921-239-01124323 – 2007 specified for steel for production of rails 350LTD. Metal macrostructure quality is satisfactory. Tensile properties, cross-section hardness, and impact strength at temperature +20 °С determined in the samples cut out from the rail head rounding-out having no contact with the wheel meet the requirements of the specifications of TU 0921-239-01124323 – 2007 for rails 350LTD. However, impact strength at sub-zero temperatures does not comply with the quality of domestic rails for low-temperature service. Nonmetallic inclusion content is not significant, however unallowable inclusions of exogenous nature have been found. The microstructure of the sample of rail produced in Japan is sorbitic and lamellar pearlite, which dispersity decreases with the increase of the distance from the surface in all elements of rail samples. When in service, slanting line cracks to 1.1 mm in depth were located on the surface of the rail head rounding-out having contact with the wheel and also considerable side wear ammounted up to 15 mm.

Effect of Temperature on Microstructure, Corrosion Resistance, and Toughness of Salt Bath Nitrided Tool Steel

In this study, a type of hot work tool steel was modified through salt bath nitriding for 4 h at 540 and 560 °C, and post-oxidation was subsequently performed. Surface and cross-sectional hardness test results revealed that the surface hardness increased after the treatment because of the formation of compound layers and diffusion zones. Microstructures and phase analyses showed that more homogeneous compound layers and Fe3O4-phase could be generated after treatment at 560 than at 540 °C. As a result, the corrosion potential was elevated, and the corrosion current density was clearly reduced. The thickness and porosity of the compound layer were also increased with the elevated nitriding temperature. Because of the nitrogen atom solution, XRD diffraction peaks broadened, and the position of the peaks shifted to a lower angle in different degrees at different depths, thus showing the same tendency as the hardness curves. Salt bath nitriding significantly deteriorated the impact toughness from 32.3 to 5.2 J.

Structure and properties of Al2O3 coatings formed on NiTi alloy by cathodic plasma electrolytic deposition

Abstract Al 2 O 3 coatings were prepared on NiTi alloy by cathodic plasma electrolytic deposition (CPED) in an aluminum nitrate solution. Scanning electron microscopy (SEM) shows that the coating exhibits a typical porous surface, rough micro structure and excellent adhesive interface between the coating and the substrate. Energy dispersive X-ray spectrometer (EDS) shows that when the treatment time is 45 min, this ceramic coating is composed of Al, O, and C with the atomic concentration of 43.37%, 48.52% and 8.11%, respectively, and the concentration of Ni is lower than the minimum instrument detection standard. X-ray diffraction (XRD) indicates that the coating consists of α-Al 2 O 3 and γ-Al 2 O 3 crystal phase. Direct pull-off test shows that the coating on NiTi substrate has a mean coating-substrate bonding strength of 15 ± 2 MPa. Cross-sectional hardness measurement illustrates that the average microhardness of the coating is less than the values of this parameter for the substrate. The results of potentiodynamic polarization test indicate that the corrosion resistance of the coated sample is increased by 3 times compared with that of the uncoated sample on the basis of corrosion current density.

Reduced hardening of nanocrystalline nickel under multiaxial indentation loading

Abstract

Formation process and cross-sectional hardness of a Cr-alloyed layer on Ti6Al4V alloy

A Cr-alloyed layer consisting of five sublayers was prepared on Ti6Al4V substrate via double glow plasma surface alloying technology at 800°C. The formation process and cross-sectional hardness of the Cr-alloyed layer were studied in detail. The results showed that a set of new phase layers (i.e., Cr, TiCr2, Ti4Cr, (βTi,Cr) and (αTi,Cr) sublayers) formed at 800°C; however, the (βTi,Cr) phase decomposed and separated out the Ti4Cr phase when the temperature decreased. Additionally, the TiCr2 phase had the highest hardness while Ti4Cr phase had the lowest hardness. Precipitation of the soft Ti4Cr phase from the (βTi,Cr) phase therefore limited the improvement of the hardness and led to an unusual change: increasing the Cr content led to a lower hardness.

Electrochemical boriding of molybdenum in molten borax

In this study, molybdenum plates (99·5% purity) were subjected to electrochemical boriding in a molten borax electrolyte in order to synthesise molybdenum boride phases on exposed surfaces. Electrochemical boriding was carried out at temperatures of 900, 950 and 1000°C for a duration of 30–180 min at a current density of 0·5 A cm−2. Cross-sectional microscopic examination of the plates indicated formation of 20 to 50 μm thick boride layers, depending on process temperature and duration. These layers consisted of two distinct boride phases: Mo2B4·027 and Mo2B5. The boride layer cross-sectional hardness was in the range of 1900–3250 HV with 50 g load. The adhesion of the boride coating to the molybdenum substrate was determined by a Rockwell C indentation adhesion test machine. The boride layers produced due to the electrochemical boriding technique were thick, hard, dense, and homogeneous.

In situ remineralizing effect of fluoride varnishes containing sodium trimetaphosphate.

This study analyzed the effects of a fluoride (F) varnish supplemented with sodium trimetaphosphate (TMP) on the remineralization of caries-like lesions in situ. Twelve subjects used palatal devices with demineralized enamel discs for 3 days, following a double-blind, crossover protocol. Test groups included placebo (no F or TMP), 5% NaF and 5% NaF/5% TMP varnishes. The percentage of surface hardness recovery (%SHR) and cross-sectional hardness (ΔKHN) were determined. Significant differences were observed among all varnishes regarding %SHR and ΔKHN. The highest %SHR and the lowest ΔKHN were seen for the 5% NaF/5% TMP varnish, followed by 5% NaF and placebo. The remineralizing effect of a 5% NaF varnish is significantly enhanced when associated with TMP. The reduction in the subsurface lesion area of enamel treated with the TMP-containing varnish implies that cavities would take longer to develop or might not develop at all depending on individual factors, resulting in lower net caries increments at individual and population levels.

Demineralization and hydrogen peroxide penetration in teeth with incipient lesions.

The aim of this study was to evaluate the demineralization and hydrogen peroxide (HP) penetration in teeth with incipient lesions submitted to bleaching treatment. For analysis of HP penetration, sound and demineralized enamel/dentin discs were placed in artificial pulp chambers containing acetate buffer solution. After bleaching treatment, this solution was subjected for analysis of optical density by spectrophotometry and the disc surfaces were analyzed with scanning electron microscopy (SEM) and polarized light microscopy (PLM). The remaining discs were subjected for cross-sectional hardness analysis at different depths. Data were analyzed by repeated measures ANOVA and PLSD Fisher test (a=0.05). It was observed that previously demineralized teeth showed greater HP penetration (p<0.05). The bleaching treatment caused changes to a depth of 20 µm in sound enamel and up to 90 µm in demineralized enamel. SEM and PLM images revealed that the bleaching treatment caused superficial changes that were considerably more accentuated in previously demineralized teeth. It may be concluded that the enamel mineralization level influences HP penetration and the bleaching agent contributed to increase the demineralization depth.

In vitro effect of sodium trimetaphosphate additives to conventional toothpastes on enamel demineralization.

The aim of this study was to evaluate the ability of conventional toothpastes (1100ppm F) supplemented with sodium trimetaphosphate (TMP) in demineralization. Blocks of enamel were selected and then divided into seven experimental groups of 12: toothpaste without F and TMP (placebo), toothpaste with 1100ppm F (1100), and toothpaste with 1100ppm F supplemented with TMP-1% (1100 1% TMP), 3% (1100 3% TMP), 4.5% (1100 4.5% TMP), 6% (1100 6% TMP), and 9% (1100 9% TMP). Blocks were subjected to five pH cycles (demineralizing/remineralizing solutions) at 37°C and treated with toothpaste slurries twice daily, after which the blocks were maintained for 2days in fresh remineralizing solution. Following treatments, surface hardness (SHf) and cross-sectional hardness were determined for calculating the integrated loss of subsurface hardness (ΔKHN). The fluoride present in the enamel was also measured. The SHf and ΔKHN measurements showed that supplementation with 3% TMP was the most effective (p < 0.001) and showed greater concentration of F in the enamel (p < 0.001). Addition of 3% TMP to a conventional toothpaste (1100ppm F) showed greater efficacy in reducing enamel demineralization. Fluoride toothpastes containing trimetaphosphate possess good anticaries potential required to reduce the prevalence of dental caries in high-risk patients.

Mechanical Property Change in the Region of Very High-cycle Fatigue

Very high-cycle fatigue behaviour of type 316L austenitic stainless steel, which is used as the structural material of the pulsed spallation neutron sources, was investigated through the ultrasonic fatigue test with the strain rate of 102 1/s. Cross-sectional hardness distributions of the fatigue-failed specimens for solution annealed (SA) and cold worked (CW) 316L were measured to understand the cyclic hardening or softening in the very high-cycle fatigue region. In addition, the tensile tests of the fatigue-failed specimens were performed at room temperature. Furthermore, the nonlinear ultrasonic system was used for evaluating the dislocation density variation during plastic deformation. The results showed the cyclic hardening in the region of very high-cycle fatigue in the case of SA 316L. In contrast, in the case of 10% CW 316L, cyclic softening occurred when the number of cycles below 106 and followed by cyclic hardening. In the case of 20% CW 316L, cyclic softening was observed when the number of cycles below 107, while cyclic hardening occurred subsequently.

In situ evaluation of low-fluoride toothpastes associated to calcium glycerophosphate on enamel remineralization

ObjectivesThis study aimed to evaluate the effect of low-fluoride toothpastes with calcium glycerophosphate (CaGP) on enamel remineralization in situ. MethodsVolunteers (n=10) wore palatal devices holding four bovine enamel blocks. The treatments involved 5 experimental phases of 3 days each according to the following toothpastes: placebo, 500ppm F (500 NaF), 500ppm F with 0.25% CaGP (500 NaF CaGP), 500ppm F with 0.25% CaGP (500 MFP CaGP) and 1100ppm F (1100; positive control). After this experimental period, the fluoride, calcium, and phosphorus ion concentrations from enamel were determined. Surface and cross-sectional hardness were also performed. Data were analysed by 1-way ANOVA, Student–Newman–Keuls’ test and by Pearson's correlation. ResultsThe addition of 0.25% CaGP improved the remineralization potential of low-fluoride toothpastes and the NaF as source of fluoride yielded the best results (p<0.001) as evidenced by the hardness analysis. The 1100ppm F toothpaste provided higher presence of fluoride in the enamel after remineralization (p<0.001). The addition of CaGP to the NaF and MFP toothpastes led to similar calcium concentration in the enamel as the observed with the positive control (p=0.054). ConclusionsToothpastes with 500ppm F (NaF or MFP) and CaGP showed similar remineralization potential than 1100ppm F toothpaste. Clinical significanceToothpastes containing 500ppm F associated to CaGP, with both fluoride source (NaF or MFP), showed a potential of remineralization similar to commercial toothpaste. Although there is a need for confirmation in the clinical setting, these results point to an alternative for improving the risk-benefit relationship between fluorosis and dental caries in small children.

Antibacterial effect of coffee: calcium concentration in a culture containing teeth/biofilm exposed to Coffea Canephora aqueous extract.

This study determined the changes of calcium concentration in a medium containing teeth/biofilm exposed to Coffea canephora extract (CCE). Enamel fragments were randomly fixed into two 24-well polystyrene plates containing BHI. Pooled human saliva was added to form biofilm on fragments. Specimens were divided into treatment groups (G, n=8 per group) and treated with 50μl daily for 1min per week, as follows: G1, 20% CCE; G2, Milli-Q water (negative control); G3, antibiotic (positive control). Six fragments represented the blank control (G4). The calcium content was observed at baseline, 4 and 7days of treatment by atomic-absorption spectrophotometry. Cross-sectional hardness of enamel was a demineralization indicator. Calcium increased in the medium after 4 and 7days of treatment in G1 (3·80±1·3mgl(-1) and 4·93±2·1mgl(-1) , respectively) and G3 (4th day=5·7±1·8mgl(-1) ; 7th day=6·7±3·5mgl(-1) ) (P>0·05). Calcium from G2 decreased after 7days, which was different from G3 (P<0·05). The lower calcium content, at the end of the experiment, was represented by G4, 2·16±0·2mgl(-1) . The increase in calcium after treatment with CCE is probably due to its antibacterial effect, which caused the bacterial lysis and consequent release of calcium in the medium. This study revealed an inhibitory action of Coffea canephora against dental biofilm. This coffee species caused bacterial lysis and consequent release of calcium into the medium. Furthermore, the advantage of coffee as an antibacterial beverage is that it is consumed in a concentrated form (6-10%) as opposed to various medicinal infusions that have shown such effect in vitro and are usually consumed at 1-2%. Therefore, a light roasted C.canephora aqueous extract can be considered as a potential anticariogenic substance.

Armor materials’ behavior under repetitive dense plasma shots

Experiments on the plasma focus device PF-12 have been carried out to investigate changes in the structure of the surface and bulk of tungsten and tungsten doped with 1% lanthanum oxide after repeated powerful deuterium plasma shots (8, 25 and 100). The surface morphology of the targets exposed to plasma streams is analyzed by electron and optical microscopy. Due to the plasma effect, different surface structures, such as wave-like structures, a melted layer, a mesh of microcracks, droplets, craters, crevices and holes, appear. The change of cross-section hardness after a number of shots in different materials is investigated.

Mechanical properties of WC–Co coatings with different decarburization levels

In this study, two kinds of WC–Co coatings with different decarburization levels were deposited by high-velocity oxy-fuel (HVOF) spraying using the ultrafine WC–Co composite powder and commercial micronsized powder, respectively. The hardness and elastic modulus were measured on the top surface and cross sections of the prepared coatings by the nanoindentation method. The results show that the ultrafine-structured coating has much higher density and inhibited decarburization than the conventional coating, which thus results in higher hardness and elastic modulus values than the micronsized coating. The wear resistance of thermal-sprayed cermet coatings greatly depends on the cross-sectional hardness and elastic modulus which reflects the bond strength between splats to some extent. Based on the analysis, a better understanding of the microstructure and properties in cermet coating materials was obtained.

In vitro Remineralizing Effect of Fluoride Varnishes Containing Sodium Trimetaphosphate

This study analyzed the effects of fluoride varnishes supplemented with sodium trimetaphosphate (TMP) on the remineralization of caries-like lesions in vitro. Bovine enamel discs were selected through surface hardness (SH) and caries-like lesions were induced. SH was again determined and the blocks were divided into 7 experimental groups (n = 24/group): placebo (no fluoride or TMP), 5% TMP, 2.5% NaF, 2.5% NaF/5% TMP, 5% NaF, 5% NaF/5% TMP and commercial formulation (Duraphat™, 5% NaF), following a blind protocol. Discs were treated with the varnishes and kept in a remineralizing solution for 4 h and a demineralizing solution for 2 h. Varnishes were then removed and half of the discs were used for analysis of loosely (CaF₂) and firmly bound fluoride. The remaining discs were submitted to a pH-cycling regimen for 6 days. The percentage of surface hardness recovery (%SHR), cross-sectional hardness (ΔKHN) and enamel CaF₂ and fluoride were determined. Data were analyzed by ANOVA and by Student-Newman-Keuls' test (p < 0.05). A dose-response relationship was observed between fluoride concentrations in the varnishes and %SHR. The 5% TMP varnish led to %SHR similar to that obtained for the placebo. When TMP was used in association with fluoride, however, significantly higher %SHR were observed in comparison with their counterparts without TMP. Moreover, ΔKHN obtained for the 5% NaF/5% TMP was significantly lower among all groups tested. Higher concentrations of CaF₂ and fluoride were observed for Duraphat and 5% NaF, followed by 5% NaF/5% TMP, 2.5% NaF and 2.5% NaF/5% TMP (p < 0.05). It was concluded that the supplementation of fluoride varnishes with TMP leads to enhanced remineralizing effect of artificial caries lesions in vitro.

Study of Quenching Organization Property under Wind Cooling Condition

In this paper, the steel of U71Mn specifications for 60kg/m heavy rail is seen as a research object. Experimental method is employed to study the heavy rail hardened layer, including surface hardness, micro-structure and cross-sectional hardness under different cooling time during quenching. Experimental results showed that obtained heavy rail after wind cooling quenching finally met the Tb/T2344-2003 43-75 kg/m standard. Best quenching treatment condition is found and the defect is reduced to large extent when quenching time is 40 seconds, cooling time is 40 to 45 seconds, superior to the traditional spray cooling condition. These results provide an important reference for the quenching process of heavy rail.

Improving the Surface Properties of Cp-Ti by Pulsed Electro-Spark Deposition

Al Ti intermetallic compounds were coated by electro-spark deposition. Commercially pure titanium (Cp-Ti) (grade 2) and aluminum rods were used as substrate and electrode materials, respectively. During the electro-spark deposition experiments the following pulse parameters in a group were used: pulse current amplitude, pulse duration and pause between the pulses of a pulse group with 100 300 500 A, 50 100 μs, and 100 μs, respectively. Al Ti coatings having a thickness range of 15 30 μm were formed on the surface of titanium substrate using electro-spark deposition process. The coating properties such as the roughness and the thickness increased with increasing pulse duration and pulse current amplitude. The mass transfer coe cient decreased with increasing pulse current amplitude and pulse duration. The quality of the adhesion characters of the coatings, determined by Rockwell-C adhesion test, becomes worse from HF-2 to HF-4, due to increase of pulse current amplitude. Depending on the electro-spark deposition process parameters, the coating formed as AlTi or as layered structure consisting of AlTi+AlTi3 when pulse current amplitude increases. The Al Ti coatings include some micro cracks lying throughout the coating from surface to interface which is nature of this process. The maximum cross-sectional hardness of the coatings were in the range of 80

Effect of resin infiltration on the nanomechanical properties of demineralized bovine enamel.

Objective:The aim of the present study was to evaluate the efficacy of resin infiltration in preventing in vitro lesion progression.Materials and Methods:Buccal surfaces of bovine incisors were divided into mesial and distal regions and, at the center, nail varnish was applied (1.0 mm width) to protect the enamel surface against any further treatment. In order to create artificial enamel lesions in the unprotected areas, each specimen was soaked in a demineralizing solution. After that, specimens had two enamel lesions. One lesion in each sample was etched with 15% HCl for 120 s and infiltrated with a commercial infiltrating resin for 3 min, while the other lesion was not treated (control). Each specimen was cross-sectionally halved and randomly allocated to two groups: Group 1 was immediately processed and Group 2 was submitted to a new demineralization process. The samples were analyzed by means of cross-sectional hardness measurements using a nanoindenter equipment. Hardness data were statistically analyzed by non-parametric Kruskal-Wallis and MannWhitney tests (α = 0.05).Results:The findings showed statistical difference between treatments at the same analyzed distance range from the outer surface of the enamel (P < 0.05).Conclusion:The untreated lesion showed lower hardness values for distances near the outer surface of the enamel. The resin infiltration was efficient in preventing further in vitro demineralization of bovine enamel lesions.

Effect of fluoride gels supplemented with sodium trimetaphosphate on enamel erosion and abrasion: In vitro study

ObjectiveThis in vitro study aims to evaluate the effect of low fluoride (F) gel associate sodium trimetaphosphate (TMP) on erosion with or without abrasion. DesignEnamel blocks (4mm×4mm) selected through surface hardness (SH) is divided into five groups (n=12): gel without F and TMP (placebo), gel containing 4500ppm F (4500), gel containing 4500ppm F plus TMP5% (4500 TMP5%), gel containing 9000ppm F (9000), and gel containing 12,300ppm F (acid gel). Those groups were additionally subdivided into conditions of erosion (Ero) and of erosion plus abrasion (Ero/Abra). The blocks have undergone a single application of gel on the first day of the study. The erosion challenge was produced by Sprite Zero® for five minutes four times a day and abrasion was carried out by machine brushing for 15s. After the challenges, the surface hardness (%SH), wear and cross-sectional hardness (ΔKHN) were analyzed. The data were analyzed using a 2-way ANOVA test followed by a Student-Newman–Keuls (p<0.05). ResultsLower values of %SH, wear and ΔKHN were observed for erosion challenge (p<0.001). The %SH was lower in groups treated with fluoride gels, differing in the placebo (p<0.05). With addition of TMP to the gel 4500, enamel wear was lower when compared with another groups (p<0.05). ConclusionIn vitro conditions, the 4500 5%TMP gel showed greatest effect against erosion and erosion/abrasion.