Vickers Hardness Change Research Articles

Effects of electrical and mechanical properties of Ba0.92Ca0.08Zr0.05Ti0.95O3 ceramics with lanthanum dopants

Element doping is one of the important approaches to improve the performance of lead-free piezoelectric ceramics. In this study, Ba0·92Ca0·08Zr0·05Ti0·95O3-xLa (BCZT-xLa) piezoelectric ceramics were prepared by sol–gel method. The effects of La3+ contents on the phase structure, mechanical properties, and electrical properties of BCZT-xLa ceramics were investigated. Results showed that La3+ could affect the properties of ceramics by adjusting the concentration of oxygen vacancies and microstructure. When the La3+ contents were 0.008, the ceramics showed the best performance (the maximum permittivity was 8736.27, the remnant polarisation was 9.69 μC/cm2 and the coercive field was 3.44 kV/cm). The influences of Vickers hardness on ceramics were investigated using various La3+ contents. The lattice energy and oxygen vacancies were the main factors for the change in Vickers hardness. With an increment of x, the Vickers hardness values decreased from 6.271 GPa to 1.438 GPa. This study could provide a reference for BCZT piezoelectric ceramics doped with rare earth elements.

Evaluation of microhardness, degree of conversion, and abrasion resistance of nanoglass and multiwalled carbon nanotubes reinforced three-dimensionally printed denture base resins.

To assess the effect of nanoglass (NG) particles and multiwalled carbon nanotubes' (MWCNTs) addition on Vickers hardness (VH), degree of conversion (DC), and abrasion resistance of 3D-printed denture base resin. 3D-printed denture base resin was reinforced using silanized NG and MWCNTs to obtain four groups: Control, 0.25 wt% NG reinforced resin, 0.25 wt% MWCNTs reinforced resin, and a combination group of 0.25 wt% of both fillers. All specimens (N = 176) were tested before and after thermal aging (600 cycles) for VH (n = 22), DC, and abrasion resistance (n = 22). Abrasion resistance specimens were subjected to 60,000 brushing strokes, and then assessed for surface roughness (Ra) and weight loss. Specimens were then scanned with a benchtop scanner before and after abrasion to produce a color map of topographical changes from superimposed images. Data were analyzed using ANOVA tests followed by Tukey post hoc test. Kruskal-Wallis test was used to compare percent change among groups, followed by Dunn post hoc test (α = 0.05). The interaction between nanofiller content and thermal cycling displayed a significant effect on VH and DC. The 0.25% NG expressed the highest VH before aging but revealed the highest percent decrease after aging. Nanofiller content, thermal aging, and brushing displayed a significant interaction impact on the Ra values. The addition of nanofillers resulted in an overall improvement in resin microhardness and abrasion resistance. The 0.25% MWCNTs group revealed the lowest Ra with the least percent change in VH and DC, while the combination one displayed the least change in weight.

Infrared transmission and refractive index dispersion of mixed-chalcogen Ge-Sb-S-Se glasses for use in molded lens applications

In an effort to augment thermal and mechanical properties of ternary Ge-Sb-Se glass for use in molded lens applications, mixed-chalcogen Ge27.5Sb12.5SxSe60-x glasses have been investigated in this study with a particular attention paid to refractive index dispersion as well as infrared transmission edge. Changes in Vickers hardness, glass transition temperature, dilatometric softening temperature and thermal expansion coefficient are elucidated in terms of structural evolutions that sulfur induces. Infrared transmission edge blueshifts upon the addition of sulfur, which can be nicely interpreted in connection with average bond energy and molar mass of a given composition based on a postulation that this glass behaves as a single average harmonic oscillator in shaping multiphonon absorption. Refractive index at the long-wavelength infrared range becomes more dispersive with increasing sulfur content in these sulfur-selenide glasses, and thereby their dispersion can be pinpointed via adjusting S content. The Abbe diagram in the long-wavelength infrared region is extended towards the high-dispersion side, thus enhancing practicality of the chalcogenide glasses as in the form of lens and/or filter for the thermal imaging applications.

Vickers hardness change of the Chinese low-activation ferritic/martensitic steel CLF-1 irradiated with high-energy heavy ions

In the present work, the irradiation hardening behavior of a Chinese low-activation ferritic/martensitic steel CLF-1, a candidate for fusion reactor blankets, is studied. Specimens were irradiated with high-energy 14N and 56Fe ions at the terminal of a cyclotron to three successively increasing damage levels of 0.05, 0.1 and 0.2 displacements per atom (dpa) at about −50 °C. The energy of the incident ions was dispersed to 11 successively decreasing grades using an energy degrader, thereby generating an atomic displacement damage plateau in the specimens from the surface to a depth of 25 μm, which is sufficiently broad for the Vickers hardness test. Eight different loads (i.e. 98 mN, 196 mN, 490 mN, 980 mN, 1.96 N, 4.9 N, 9.8 N and 19.6 N) were applied to the specimens to obtain the depth profiles of the Vickers hardness by using a micro-hardness tester. Hardening was observable at the lowest damage level, and increased with increasing irradiation dose. A power-law correlation of the Vickers hardness with the damage level (HV0 = 1.49 + 0.76 dpa0.31) is proposed. Testing with a nano-indentation technique was also performed, and a linear relationship between the Vickers micro-hardness and the nano-hardness (HV0 = 0.83H0) was observed. A comparison with other RAFM steels (CLAM, JLF-1, F82H, EUROFER97 etc.) under neutron or charged particle irradiation conditions shows that most of the RAFM steels exhibit similar power-law exponents in the dose dependence of irradiation hardening. The difference in the irradiation hardening may be attributed to differences in microstructure prior to irradiation.

Influence of cryo-processing on properties of tungsten carbide with low, medium and high cobalt content

This research was designed to evaluate the influence of cryo-processing on properties of tungsten carbide with varied cobalt content. Samples of uncoated tungsten carbide with 6% (WC-6 wt%Co), 9% (WC-9 wt%Co) and 25% cobalt (WC-25 wt%Co) content were fabricated for the research. Magnetic properties, porosity analysis, eta phase analysis by microscopic observation, EDS, XRD and Vickers hardness were evaluated. Investigation shows that 25% cobalt content samples after cryo-processing exhibit a significant improvement of around 2.2% in Vickers hardness and 8.7% in coercivity followed by samples with 9% cobalt grade (1.2% increase in Vickers hardness and 2.1% in coercivity), whereas 6% cobalt samples showed negligible changes. There is no change in the other properties in any of the selected grades. The change in Vickers hardness and coercivity are attributed to the cobalt’s phase transformation from FCC to HCP structure in cryo-processed samples. This study reveals that the amount of cobalt used in the fabrication of tungsten carbide tools is the determinant factor for the changes in properties.

Application of highly sensitive spectrophotometric analysis in detection of metal content in molybdenum reinforced alumina obtained by precursor infiltration of ceramic preforms

The competitive method for the preparation of molybdenum reinforced alumina has been proposed and investigated as a model for obtaining metal reinforced ceramics. The proposed method consists of infiltration of porous ceramic preform with a solution of metallic precursor followed by sintering combined with the reduction of deposited salt. This method enables formation of the composites that exhibit 36% improvement in compressive strength and no significant change in Vickers hardness in comparison to pure alumina with addition of only 0.22 wt% of molybdenum. Obtained results showed that the deposited metal concentration is highly correlated with the concentration of the precursor solution. In order to precisely determine the amount of molybdenum in the samples unconventional and novel method based on the UV/VIS spectrophotometry has been developed. This method shows a good detection ability that is suitable for determination of small amounts of metal below 0.5 wt% - a quantity difficult to analyse by using classic methods such as energy-dispersive X-ray spectroscopy (EDS).

Continuous Cooling Phase Transformation Rule of 20CrMnTi Low-Carbon Alloy Steel

Gear steel is a ferritic steel. In the rolling process, the ideal structure is ferrite + pearlite, and bainite or martensite is not expected. However, due to the high alloy content, the hardenability is good, and the bainite or martensite structure is very likely to be generated upon cooling after rolling. In this paper, phase transformation rules during continuous cooling of 20CrMnTi with and without deformation were studied to guide the avoidance of the appearance of bainite or martensite in steel. A combined method of dilatometry and metallography was adopted in the experiments, and the dilatometer DIL805A and thermo-simulation Gleeble3500 were used. Both dynamic and static continuous cooling transformation (CCT) diagrams were drawn by using the software Origin. The causes of those changes in starting temperature, finishing temperature, starting time and transformation duration in ferrite-pearlite phase transformation were analyzed, and the change in Vickers hardness of samples with different cooling rate was discussed. The results indicate that with different cooling rate, there are three phase transformation zones: ferrite-pearlite, bainite and martensite. Deformation of austenite accelerates the occurrence of transformation obviously and moves CCT curve to left and up direction. When the cooling rate is lower than 1 °C/s, the phases in samples are mainly ferrite and pearlite, which is the ideal microstructure of experimental steel. As the cooling rate increases, starting temperature of ferrite transformation in steel decreases, starting time reduces, transformation duration gradually decreases, and the Vickers hardness of samples increases. Under the cooling rate of 0.5 °C/s, ferrite transformation in deformed sample starts at 751.67 °C, ferrite-pearlite phase transformation lasts 167.9 s, and Vickers hardness of sample is 183.4 HV.

Effects of Ti Sheet Insert on Microstructure and Properties of Graded Composites of TiB2-based Ceramic and Ti-6Al-4V Alloy

By inserting Ti sheet between ceramic powder and Ti alloy steel, (TiC-TiB2)/Ti-6Al-4V graded composites were rapidly prepared by SHS centrifugal-casting process with different Ti sheet thickness from 0.5 to 1.5 mm. XRD, FESEM and EDS results show that there is no significant change in phase composition of the ceramic matrix after inserting Ti sheet, but the inserting promotes the microstructure refinement of the reaction products with the thickness increasing. Meanwhile, the introduction of Ti sheet not only enhances the thickness of the gradient interface, but also decreases the thermal infected zone of interface. Moreover, fusion bonding and atomic interdiffusion between liquid TiC-TiB2 and excessive Ti liquid in thermal vacuum circumstances are considered to initiate peritectic reaction of TiB2(s) + Ti(l) → 2TiB(s), direct growth of TiB solids from liquid Ti and eutectic reaction of TiB solids and liquid Ti at the final stage of joint solidification, so that consumption of TiB2 solids and increase of TiB crystal relieve the interface residual stress, and the joint of the ceramic to Ti alloy is achieved in multilevel and multi-scale microstructure. The joint represents a transitional change in Vickers hardness and gets a high shear strength of (316±25) MPa between the ceramic and Ti alloy.

Change in Mechanical Strength and Bone Contact Ratio of Beta-Type TNTZ Subjected to Mechanical Surface Modification

Ti-29Nb-13Ta-4.6Zr (TNTZ), which is one of metastable beta-type Ti alloys, has developed as one of representative biomedical and dental Ti alloys in Japan. TNTZ subjected to solution treatment shows Young’s modulus of 60 GPa, which is close to that of cortical bone. In addition, TNTZ has very low cytotoxicity and good bone biocompatibility as well. Heat treatment like solution treatment and aging (STA) is mainly used for improving the mechanical properties of metastable beta-type Ti alloys because of alpha precipitates, while Young’s modulus also rises drastically. This study was investigated the effects of mechanical surface modifications such as fine particle bombarding (FPB) with steel and hydroxyapatite particles or friction stir processing (FSP) on the mechanical strength of TNTZ in order to maintain low Young’s modulus. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ subjected to FPB of steel particles were also evaluated. Vickers hardness (HV) of TNTZ subjected to FPB with fine particles of steel and hydroxyapatite particles increased by HV30 to 200 at the edge of the specimen surface to around 100 to 300 mm in depth as compared with that of TNTZ subjected to solution treatment. The hydroxyapatite layer was formed on the specimen surface by FPB with fine particles of hydroxyapatite particles, although the trend was not significant by FPB with steel particles. Furthermore, the fatigue strength in high cycle fatigue region of TNTZ subjected to FPB with steel particles was improved and the fatigue limit showed around 400 MPa, although that of TNTZ subjected to FPB with fine particles of hydroxyapatite particles were around 60 MPa higher than that to TNTZ subjected to solution treatment (230 MPa). TNTZ with a rough surface texture (Ra: 0.65 μm) showed a relative bone contact ratio of more than 80% after undergoing FPB with fine particles of steel particles; this value was significantly higher than that of TNTZ with a surface texture (Ra: 0.07 μm). Lastly, the microstructure of TNTZ subjected to FSP showed the recrystallization area by the frictional heating with very fine equiaxed beta phase with an average grain diameter of 3.0 μm. The change in Vickers hardness of TNTZ subjected to FSP was almost identical to that of Young’s modulus and showed the almost same trend of FPB.

Changes in Vickers hardness during the decomposition of bone: Possibilities for forensic anthropology

The purpose of this study was to determine how the Vickers hardness (HV) of bone varies during soft tissue putrefaction. This has possible forensic applications, notably for determining the postmortem interval. Experimental porcine bone samples were decomposed in surface and burial deposition scenarios over a period of 6 months. Although the Vickers hardness varied widely, it was found that when transverse axial hardness was subtracted from longitudinal axial hardness, the difference showed correlations with three distinct phases of soft tissue putrefaction. The ratio of transverse axial hardness to longitudinal axial hardness showed a similar correlation. A difference of 10 or greater in HV with soft tissue present and signs of minimal decomposition, was associated with a decomposition period of 250 cumulative cooling degree days or less. A difference of 10 (+/- standard error of mean at a 95% confidence interval) or greater in HV associated with marked decomposition indicated a decomposition period of 1450 cumulative cooling degree days or more. A difference of −7 to +8 (+/- standard error of mean at a 95% confidence interval) was thus associated with 250 to 1450 cumulative cooling degree days’ decomposition. The ratio of transverse axial HV to longitudinal HV, ranging from 2.42 to 1.54, is a more reliable indicator in this context and is preferable to using negative integers These differences may have potential as an indicator of postmortem interval and thus the time of body deposition in the forensic context.

Direct laser deposition of Ti-6Al-4V from elemental powder blends

Purpose This paper aims to achieve Ti-6Al-4V from Ti, Al and V elemental powder blends using direct laser deposition (DLD) and to understand the effects of laser transverse speed and laser power on the initial fabrication of deposit’s microstructure and Vickers hardness. Design/methodology/approach Two sets of powder blends with different weight percentage ratio for three elemental powder were used during DLD process. Five experiments with different processing parameters were performed to evaluate how microstructure and Vickers hardness change with laser power and laser transverse speed. Energy dispersive X-ray spectroscopy, optical microscopy and Vickers hardness test were used to analyze deposits’ properties. Findings This paper reveals that significant variance of elemental powder’s size and density would cause lack of weight percentage of certain elements in final part and using multiple coaxial powder nozzles design would be a solution. Also, higher laser power or slower laser transverse speed tend to benefit the formation of finer microstructures and increase Vickers hardness. Originality/value This paper demonstrates a new method to fabricate Ti-6Al-4V and gives out a possible weight percentage ratio 87:7:6 for Ti:Al:V at powder blends during DLD process. The relationship between microstructure and Vickers hardness with laser power and laser transverse speed would provide valuable reference for people working on tailoring material properties using elemental powder method.

치약용 약효제의 적용시간에 따른 실험실적 효능 연구

페이스트 치약의 구강 내 사용시간(1~3분)과 사용시간을 길게 조절할 수 있는 부착형 치약의 사용시간을 고려하여 치약제의 유효성분을 처리시간 조건별로(1분, 3분, 10분, 30분 및 60분) 미백 효과, 항치석 효과, 재광화 효과 및 상아세관의 폐쇄 효과를 실험실적으로 평가한 결과 다음과 같은 결과를 도출하였다. 처리 시간대별 명도 변화값(<TEX>${\Delta}L$</TEX>)은 1분 <TEX>$5.50{\pm}1.51$</TEX>에서 60분 <TEX>$27.35{\pm}0.54$</TEX>였고 치석으로부터 제거된 칼슘 양(ppm)은 1분 <TEX>$4.23{\pm}0.14$</TEX>에서 60분 <TEX>$25.15{\pm}0.32$</TEX>였으며 경도 증가값은 1분 <TEX>$1.96{\pm}1.44$</TEX>에서 60분 <TEX>$12.55{\pm}2.09$</TEX>였다. 상아세관의 폐쇄 정도는 10분 처리에서 일부 상아세관의 폐쇄가 관찰되기 시작하여 60분 처리에서는 대부분의 상아세관의 폐쇄가 관찰되었다. 본 실험조건에서는 처리시간을 10분에서 60분 처리시 1분에서 3분 처리할 때보다 최소 1.57배에서 최대 8.26배까지 효능을 증가시켰으며 재광화 효과, 항치석 효과 및 상아세관 폐쇄 효과에서는 사용시간 10분 이상에서 적절하였고 미백효과에서는 30분 이상이 보다 효과적일 것으로 생각되었다. The purpose of this study was to evaluate the in-vitro efficacy of the active ingredients of dentifrice following treatment time. The whitening effect was evaluated by a change in lightness value relative to the contact time of hydrogen peroxide, by using artificially stained hydroxyapatite discs. The anti-calculus effect was assessed based on the amount of calcium eluted from the human dental calculus by sodium pyrophosphate. Remineralization was evaluated by the Vickers hardness test following the application of sodium fluoride to bovine enamel. In order to view dentinal tubules occlusion, the formation of insoluble calcium salts by bovine dentin specimens was observed using scanning electron microscopy. Change in lightness value (<TEX>${\Delta}L$</TEX>) was <TEX>$5.50{\pm}1.51$</TEX> after 1 min of treatment, <TEX>$5.73{\pm}0.43$</TEX> after 3 min, <TEX>$8.64{\pm}0.24$</TEX> after 10 min, <TEX>$18.93{\pm}0.76$</TEX> after 30 min, and <TEX>$27.35{\pm}0.54$</TEX> after 60 min. The amount of calcium eluted from the human dental calculus was <TEX>$4.23{\pm}0.14ppm$</TEX> after 1 min of treatment, <TEX>$4.51{\pm}0.04ppm$</TEX> after 3 min, <TEX>$12.12{\pm}0.16ppm$</TEX> after 10 min, <TEX>$17.85{\pm}0.81ppm$</TEX> after 30 min, and <TEX>$25.15{\pm}0.32ppm$</TEX> after 60 min. The Vickers hardness change value (<TEX>${\Delta}VHN$</TEX>) was <TEX>$1.96{\pm}1.44$</TEX> after 1 min, <TEX>$1.52{\pm}1.06$</TEX> after 3 min, <TEX>$9.06{\pm}0.15$</TEX> after 10 min, <TEX>$10.83{\pm}5.13$</TEX> after 30 min, and <TEX>$12.55{\pm}2.09$</TEX> after 60 min. Partial dentinal tubules occlusion was observed at 10 min and complete occlusion was evident at 60 min. In summary, the use of patch type dentifrices for 10, 30, or 60 min were 1.57 to 8.26 times more effective than using the paste type dentifrices for 1 to 3 min. Based on these findings, it is reasonable to expect that the use of patch type dentifrices for 10 min would lead to remineralization, anti-calculus and dentinal tubules occlusion effects, and that use for 30 min would result in a whitening effect.

Combustion Synthesis of TiB2-TiC/42CrMo4 Composites with Gradient Joint Prepared in Different High-Gravity Fields

The novel TiB2-TiC/42CrMo4-laminated composite materials were successfully fabricated by combustion synthesis in different high-gravity fields. This ceramic/metal composite material possesses continuously graded composition, and multilevel gradient microstructure, which is composed of TiB2-TiC ceramic substrate, ceramic-based intermediate layer, metal-based intermediate layer, and 42CrMo4 substrate. The ceramic-based intermediate layer is the main gradient transition region in the joint which shows that the TiB2 and TiC grains decrease gradually in size and volume fraction from the ceramic substrate to metal substrate. The experiment reveals that the increased high-gravity field not only leads to the higher combustion temperature and the remarkable thermal explosion mode, but also attributes to the enhanced interdiffusion and convection between the molten steel surface and liquid TiB2-based ceramic. So, the reliable fusion bonding of TiB2-TiC/42CrMo4 composite materials is achieved. Moreover, the phase separation and forced filling effect of high-gravity field is the key to improve the densification and bond performance of the joint. The ceramic/metal joint in the continuous gradient composition and microstructure represents not only the transitional change of Vickers hardness, but also the high shear bond strength of 420 ± 25 MPa.

Influence of consolidation process and sintering temperature on microstructure and mechanical properties of near nano- and nano-structured WC-Co cemented carbides

In this paper the influence of the consolidation process and sintering temperature on the properties of near nano- and nano-structured cemented carbides was researched. Samples were consolidated from a WC 9-Co mixture by two different powder metallurgy processes; conventional sintering in hydrogen and the sinter-HIP process. Two WC powders with different grain growth inhibitors were selected for the research. Both WC powders used were near nanoscaled and had a grain size of 150nm and a specific surface area of 2.5m2/g. Special emphasis was placed on microstructure and mechanical properties; hardness and fracture toughness of sintered samples. Consolidated samples are characterised by different microstructural and mechanical properties with respect to the sintering temperature, the consolidation process used and grain growth inhibitors in starting powders. Increasing sintering temperature leads to microstructure irregularities and inferior hardness, especially for samples sintered in hydrogen. The addition of Cr3C2 in the starting powder reduced a carbide grain growth during sintering, improved microstructural characteristics, increased Vickers hardness and fracture toughness. The relationship between hardness and fracture toughness is not linear. Palmqvist toughness does not change with regard to sintering temperature or the change of Vickers hardness.

Energetic ion beam induced crystal phase transformation and resulting hardness change in Ni3Al intermetallic compound

The Ni3Al bulk intermetallic compound was irradiated with 5.4-MeV Al, 10-MeV I and 16-MeV Au ions at room temperature. The effect of irradiation on the lattice structure was observed by X-ray diffraction (XRD). The change in Vickers hardness by irradiation was estimated. A crystal structure analysis showed that, the Ni3Al lattice structure transforms from an ordered L12 lattice structure to a disordered A1 (fcc) lattice structure by energetic ion irradiation. The relative degree of order correlates well with the density of energy that was elastically deposited by irradiation. The Vickers hardness tends to decrease with an increase in ion fluence. The hardness is not correlated with the elastically deposited energy. The effect of annealing at elevated temperatures on the irradiation induced crystal phase transformation and the Vickers hardness is also discussed.

Microstructure and mechanical properties of cold-rolled Ti50Ni47Fe3 shape memory alloy

Mechanical and shape memory properties of a Ti50Ni47Fe3 alloy annealed at 450-750 °C for 1 h after a cold-rolled reduction of 25% were investigated by phase transformation analysis and microstructure characterization using tensile tests, Vickers hardness tests, electrical resistivity-temperature tests, SEM and TEM. From the results of the tensile, it can be inferred that the fracture stress and yield stress decreased and the fracture elongation increased as the annealing temperature increased for the rolled Ti50Ni47Fe3 alloy. They reached stead values when the temperature was above 650 °C. The change in Vickers hardness corresponded to the change in the fracture stress and yield stress. The electrical resistivity-temperature curves suggest that a two- stage martensitic transformation (B2-R-B19') occurred during cooling and heating. The transformation temperatures decreased to lower temperatures when the annealing temperature was increased and maintained the same after the annealing temperature reached 650 °C. TEM revealed the distinct processes occurring at elevated temperatures: recovery, polygonization, and recrystallization.

Effects of irradiation induced Cu clustering on Vickers hardness and electrical resistivity of Fe–Cu model alloys

Three kinds of Fe-based model alloys, Fe–0.018 atomic percent (at.%) Cu, Fe–0.53at.%Cu, and Fe–1.06at.%Cu were irradiated with 2MeV electrons up to the dose of 2×10−5dpa at 250°C. After the irradiation, the increase in Vickers hardness and the decrease in electrical resistivity were observed. The increase in hardness by electron irradiation is proportional to the product of the Cu contents and the square root of the electron dose. The decrease in electrical resistivity is proportional to the product of the square of Cu contents and the electron dose.Cu clustering in the materials with electron irradiation and thermal aging was observed by means of the Atom Probe Tomography (APT). The change in Vickers hardness and electrical resistivity is well correlated with micro-structure evolution related to the Cu clustering process. The irradiation hardening was proportional to the square root of volume fraction of the Cu clusters from early stage of irradiation.

Fusion bonding of solidified TiC–TiB2 ceramic to Ti–6Al–4V alloy achieved by combustion synthesis in high-gravity field

By taking combustion synthesis in high-gravity field to prepare the solidified TiC–TiB2 ceramic, a novel and available strategy for achieving the joint of near-full-density fine-grained TiC–TiB2 ceramic to Ti–6Al–4V alloy in continuously-graded composition was discussed. The presence of microstructure transformation rather than a clear interface in the joint was considered a result of the achievement of the joint in multilevel and multiscale, which characterized by the size and the distribution of TiB phases. Fusion bonding and atomic interdiffusion between liquid TiC–TiB2 and liquid Ti in thermal vacuum circumstances were considered to initiate peritectic reaction of TiB2(s)+Ti(l)→TiB(s), direct growth of TiB solids from liquid Ti and eutectic reaction of TiB solids and liquid Ti at the final stage of joint solidification, successively, so that consumption of TiB2 solids and the decrease of TiB crystals in size and volume both occurred, and the joint of the ceramic to Ti alloy was achieved in multilevel and multiscale. The joint in continuously graded composition and microstructure represents not only a transitional change of Vickers hardness but also the high shear strength of 450±25MPa between the solidified ceramic and Ti alloy, and shear fracture usually happen at the solidified area of HAZ (heat-affected zone) due to the presence of the coarsened α′-Ti martensitic grains and shrinkage cavities.

Microstructural Change of β′ Phase and Hardness Change in As-Solutionized Dental Ag-20Pd-12Au-14.5Cu Alloy

Change in the Microstructure of the L10-Type Ordered β' Phase Precipitated in Ag-20Pd-12Au-14.5Cu Alloy (mass%) Subjected to Solution Treatment with Varying Solution Treatment Time Was Investigated. The Size of the β' Phase Is Found to Decrease with Increasing Solution Treatment Time and the Vickers Hardness of the Alloy after Solution Treatment Decreases. Experimental Observations Show that the Microstructural Change of the β' Phase Strongly Contributes to the Change in Vickers Hardness. In Addition, the Formation and Growth of the β' Phase Are Concluded to Be Affected by the Distribution of Elements through Solution Treatment.

치과용(齒科用) 순(純) 타이타늄 스크랩을 재활용(再活用)한 Ti-6Al-4V 합금(合金)의 제조(製造) 및 산소(酸素) 제어(制御)

본 연구는 치과용 순 타이타늄 스크랩을 재활용하여 진공 아크 용해에 의해 Ti-6Al-4V 합금을 제조하였고, 이때 산소함량이 다르게 제조된 Ti-6A1-4V 합금의 물성을 평가하였다. 사용된 타이타늄 스크랩은 치과용 임플란트 재료로써 ASTM G1~G4 등급으로 산소함량이 다르게 진공 아크 용해에 의해 건전한 잉곳을 만든 후 Ti-6Al-4V 합금을 제조하였다. 합금 제조시 875 torr의 가압 아르곤 분위기에서 용해하였을 때 Al 조성의 손실이 방지됨을 확인하였다. 제조된 Ti-6Al-4V의 산소함량이 1170~3340 ppm으로 증가함에 따라 Ti-6Al-4V의 경도가 증가하여 순 타이타늄의 경향과 동일함을 확인하였다. 따라서 본 연구를 통해서 Ti-6Al-4V 합금 제조에 있어서 진공 아크 용해에 의해 치과용 순 타이타늄 스크랩의 재활용 가능성을 확인하였다. The Ti-6Al-4V alloys were prepared by recycling of dental Ti pure scraps using vacuum arc melting process, and their physical properties were evaluated the Ti-6Al-4V alloys with different oxygen concentrations. For the preparation of Ti-6Al-4V alloys, Ti pure scraps used for dental implant were utilized as a raw material, and their different oxygen concentrations were ranged from G1 to G4 grade in ASTM standards. It was confirmed that the weight loss of Al in the composition of Ti-6Al-4V alloy could be controlled under the Ar pressure of 875 torr during the melting of alloy. The oxygen concentrations of the Ti-6Al-4V alloys were ranged from 1170 to 3340 ppm. The vickers hardness change of the Ti-6Al-4V alloys showed a similar behavior with that of pure Ti. As a result, we confirmed a possibility of preparation of Ti-6Al-4V alloy by recycling of dental Ti scraps using vacuum arc melting process in this study.