The aerospace and power generation industries have an increasing demand for high-temperature, highstrength materials. However, conventional materials typically lack sufficient fracture toughness and oxidation resistance at high temperatures. This study aims to enhance the high-temperature properties of Nb-Si-Ti alloys through ball milling. To analyze the effects of milling time, the progression of alloying is evaluated on the basis of XRD patterns and the microstructure of alloy powders. Spark plasma sintering (SPS) is employed to produce compacts, with thermodynamic modeling assisting in predicting phase fractions and sintering temperature ranges. The changes in the microstructure and variation in the mechanical properties due to the adjustment of the sintering temperature provide insights into the influence of Nb solid solution, Nb5Si3, and crystallite size within the compacts. By investigating the changes in the mechanical properties through strengthening mechanisms, such as precipitation strengthening, solid solution strengthening, and crystallite refinement, this study aims to verify the applicability of Nb-Si-Ti alloys in advanced material systems.

Recently, high-entropy carbides have attracted considerable attention owing to their excellent physical and chemical properties such as high hardness, fracture toughness, and conductivity. However, as an emerging class of novel materials, the synthesis methods, performance, and applications of high-entropy carbides have ample scope for further development. In this study, equiatomic (Hf-Ti-Ta-Zr-Nb)C high-entropy carbide powders have been prepared by an ultrahigh- energy ball-milling (UHEBM) process with different milling times (1, 5, 15, 30, and 60 min). Further, their refinement behavior and high-entropy synthesis potential have been investigated. With an increase in the milling time, the particle size rapidly reduces (under sub-micrometer size) and homogeneous mixing of the prepared powder is observed. The distortions in the crystal lattice, which occur as a result of the refinement process and the multicomponent effect, are found to improve the sintering, thereby notably enhancing the formation of a single-phase solid solution (high-entropy). Herein, we present a procedure for the bulk synthesis of highly pure, dense, and uniform FCC single-phase (Fm3m crystal structure) (Hf-Ti-Ta-Zr-Nb)C high-entropy carbide using a milling time of 60 min and a sintering temperature of 1,600oC.

This study explores reducing the oxygen content of a commercial Ti-48Al-2Cr-2Nb powder to less than 400 ppm by deoxidation in the solid state (DOSS) using Ca vapor, and investigates the effect of Ca vapor on the surface chemical state. As the deoxidation temperature increases, the oxygen concentration of the Ti-48Al-2Cr-2Nb powder decreases, achieving a low value of 745 ppm at 1100oC. When the deoxidation time is increased to 2 h, the oxygen concentration decreases to 320pp m at 1100oC, and the oxygen reduction rate is approximately 78% compared to that of the raw material. The deoxidized Ti-48Al-2Cr-2nb powder maintains a spherical shape, but the surface shape changes slightly owing to the reaction of Ca and Al. The oxidation state of Ti and Al on the surface of the Ti-48Al-2Cr-2Nb powder corresponds to a mixture of TiO2 and Al2O3. As a result, the peaks of metallic Ti and Ti suboxide intensify as TiO2 and Al2O3 in the surface oxide layer are reduced by Ca vapor deposition

In this study, we report the microstructure and characterization of Ta20Nb20V20W20Ti20 high-entropy alloy powders and sintered samples. The effects of milling time on the microstructure and mechanical properties were investigated in detail. Microstructure and structural characterization were performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the sintered samples were analyzed through a compressive test at room temperature with a strain rate of 1 × 10−4 s−1. The microstructure of sintered Ta20Nb20V20W20Ti20 high-entropy alloy is composed of a BCC phase and a TiO phase. A better combination of compressive strength and strain was achieved by using prealloyed Ta20Nb20V20W20Ti20 powder with low oxygen content. The results suggest that the oxide formed during the sintering process affects the mechanical properties of Ta20Nb20V20W20Ti20 high-entropy alloys, which are related to the interfacial stability between the BCC matrix and TiO phase.

Piezoelectric ceramic specimens with the Pb(Mg1/3Nb2/3)0.65Ti0.35O3 (PMN-PT) composition are prepared by the solid state reaction method known as the “columbite precursor” method. Moreover, the effects of the Li2O-Bi2O3 additive on the microstructure, crystal structure, and piezoelectric properties of sintered PMN-PT ceramic samples are investigated. The addition of Li2O-Bi2O3 lowers the sintering temperature from 1,200oC to 950oC. Moreover, with the addition of >5 wt.% additive, the crystal structure changes from tetragonal to rhombohedral. Notably, the sample with 3 wt.% additive exhibits excellent piezoelectric properties (d33 = 596 pC/N and Kp = 57%) and a sintered density of 7.92 g/cm3 after sintering at 950oC. In addition, the sample exhibits a curie temperature of 138.6oC at 1 kHz. Finally, the compatibility of the sample with a Cu electrode is examined, because the energy-dispersive X-ray spectroscopy data indicate the absence of interdiffusion between Cu and the ceramic material.

Titanium and its alloys are useful for implant materials. In this study, porous Ti-Nb-Zr biomaterials were successfully synthesized by powder metallurgy using a NH4HCO3 as space holder and TiH2 as foaming agent. Consolidation of powder was accomplished by spark plasma sintering process(SPS) at 850˚C under 30 MPa condition. The effect of high energy milling time on pore size and distribution in Ti-Nb-Zr alloys with space holder(NH4HCO3) was investigated by optical microscope(OM), scanning electron microscope(SEM) & energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). Microstructure observation revealed that, a lot of pores were uniformly distributed in the Ti-Nb-Zr alloys as size of about 30-100μm using mixed powder and milled powders. In addition, the pore ratio was found to be about 5-20% by image analysis, using an image analyzer(Image Pro Plus). Furthermore, the physical properties of specimens were improved with increasing milling time as results of hardness, relative density, compressive strength and Young's modulus. Particularly Young's modulus of the sintered alloy using 4h milled powder reached 52 GPa which is similar to bone elastic modulus.

To improve coating ability and the life of the coating, Ti based composite materials with hydroxyapatite(HA) should be developed. The raw materials of Ti-26wt%, Nb-1wt%, and Si with 10wt% HA were mixed for 24 h by a mixing machine and milled for 1 h to 6 h by planetary mechanical ball milling. Ti-26%Nb-1%Si-(10%HA) composites, composed of nontoxic elements, were fabricated successfully by spark plasma sintering(SPS) at 1000˚C under 70MPa. The relative density of the sintered Ti-Nb-Si-HA composites using the 24 h mixed powder, and the 6 h milled powder, was 91% and 97 %, respectively. The effects of HA contents and milling time on microstructure and mechanical properties were investigated by SEM and hardness tester, respectively. The Vickers hardness of the composites increased with increasing milling time and higher HA content. The Young's modulus of the sintered Ti-26%Nb-1%Si-10%HA composite using the 6 h-milled powder was 55.6 GPa, as obtained by compression test. Corrosion resistance of the Ti-26wt%Nb-1wt%Si composite was increased by milling and by the addition of 10wt%HA. Wear resistance was improved with increasing milling time. Biocompatibility of the Ti-Nb-Si alloys was improved by the addition of HA.

The Ti-6Al-4V extra low interstitial (ELI) alloy has been widely used as an orthopedic implant material because of its excellent mechanical properties and biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity of the Al and V elements. Therefore, non-toxic biomaterials with a low elastic modulus need to be developed. A high energy mechanical milling (HEMM) process is introduced to improve the effect of sintering. Rapid sintering of spark plasma sintering (SPS) under pressure was used to make an ultra fine grain of Ti-25 wt.%Nb-7 wt.%Zr-10 wt.%Mo-(10 wt.%CPP) composites with bio-attractive elements for increasing strength. These composites were fabricated by SPS at 1000˚C at 60 MPa using HEMM powders. During the sintering process, CaTiO3, TixOy, and CaO were formed because of the reaction between Ti and CPP. The effects of CPP content on the physical and mechanical properties of the sintered Ti-Nb-Zr-Mo-CPP composites were investigated. The biocompatibility and corrosion resistance of the Ti-Nb-Zr-Mo alloys were improved by the addition of CPP.

Ti-6Al-4V ELI (Extra Low Interstitial) alloy have been widely used as alternative to bone due to its excellent biocompatibility, although it still has many problems such as high elastic modulus and toxicity. Therefore, biomaterials with low elastic modulus and non toxic characteristics have to be developed. A novel β Ti-35wt%Nb-7wt%Zr-Calcium pyrophosphate (CPP) composite that is a biocompatible alloy without elemental Al or V was fabricated by spark plasma sintering (SPS) at 1000˚C under 70 MPa using high energy mechanical milled (HEMM) powder. The microstructure and phases of the milled powders and the sintered specimens were studied using SEM, TEM, and XRD. Ti-35wt%Nb-7wt%Zr alloy was transformed from α phase to β phase in the 4h-milled powder by sintering. The sintered specimen using the 4h-milled powder showed that all the elements were distributed very homogeneously and had higher density and hardness. β Ti alloy-CPP composite, which has nanometer particles, was fabricated by SPS using HEMMed powder. During the sintering process, CaTiO3, TixOy, and CaO were formed because of the reaction between Ti and CPP. The Vickers hardness of the composites increases with the increase of the milling time and the addition of CPP. The biocompatibility of the Ti-Nb-Zr alloys was improved by addition of CPP.

니오븀 금속을 기반으로 하는 Nb56Ti23Ni21 합금 분리막의 수소 투과 특성 및 화학적 안정성에 관한 연구를 수행하였다. 이를 위하여 직경 10 mm, 두께 0.5 mm의 Nb56Ti23Ni21 합금 분리막을 제작하였으며, 2가지 조성(H2 100%, H2 60% + CO2 40%)의 공급가스를 450℃의 온도에서 투과시킬 때 압력에 따른 수소 투과 특성에 관한 실험을 진행하였다. 본 실험에서의 최대 수소 투과량은 순수한 수소를 투과시킬 경우 절대압력 3 bar에서 5.58mL/min/cm2로 나타났다. 또한 공급가스 조성에 따른 각각의 경우 모두 Sievert's law에 잘 부합하였으며, 이산화탄소와의 혼합가스 사용시, 투과량은 수소 분압 감소에 비례하여 감소하였다. 투과 실험 후 XRD 분석을 통하여 Nb56Ti23Ni21 합금 분리막의 이산화탄소에 대한 화학적 안정성에 대한 실험을 수행하였다.

The effect of oxygen on the shape memory characteristics in Ti-18Nb-6Zr-XO (X = 0-1.5 at%) biomedical alloys was investigated by tensile tests. The alloys were fabricated by an arc melting method at Ar atmosphere. The ingots were cold-rolled to 0.45 mm with a reduction up to 95% in thickness. After severe cold-rolling, the plate was solution-treated at 1173 K for 1.8 ks. The fracture stress of the solution-treated specimens increased from 450 Mpa to 880 MPa with an increasing oxygen content up to 1.5%. The fracture stress increased by 287MPa with 1 at% increase of oxygen content. The critical stress for slip increased from 430 MPa to 695 MPa with an increasing oxygen content up to 1.5 at%. The maximum recovery strain of 4.1% was obtained in the Ti-18Nb-6Zr-0.5O (at%) alloy. The martensitic transformation temperature decreased by 140 K with a 1.0 at% increase in O content, which is lower than that of Ti-22Nb-(0-2.0)O (at%) by 20 K. This may have been caused by the effect of the addition of Zr. This study confirmed that addition of oxygen to the Ti-Nb-Zr alloy increases the critical stress for slip due to solid solution hardening without being detrimental to the maximum recovery strain.

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at 1000˚C under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. Ti2O, CaO, CaTiO3, and TixPy phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

The aim of this study was to investigate microstructures and mechanical properties of nano-sized Ti-35 wt.%Nb-7 wt.%Zr-10 wt.%CPP composite fabricated by high energy mechanical milling (HEMM) and pulse current activated sintering (PCAS). Grain growth of the mechanically milled powder was prevented by performing PCAS. The principal advantages of calcium phosphate materials include: similarity in composition to the bone mineral, bioactivity, osteoconductivity and ability to form a uniquely strong interface with bone. The hardness and wear resistance property of nano-sized Ti-35 wt.%Nb-7 wt.%Zr-10 wt.%CPP composites increased with increasing milling time because of decreased grain-size of sintered composites.

The phase Ti-Nb-Sn-HA bio materials were successfully fabricated by high energy mechanical milling and pulse current activated sintering (PCAS). Ti-6Al-4V ELI alloy has been widely used as biomaterial. But the Al has been inducing Alzheimer disease and V is classified as toxic element. In this study, ultra fine sized Ti-Nb-Sn-HA powder was produced by high energy mechanical milling machine. The phase Ti-Nb-Sn-HA powders were obtained after 12hr milling from phase. And ultra fine grain sized Ti-Nb-Sn-HA composites could be fabricated using PCAS without grain growth. After sintering, the microstructures and phase-transformation of Ti-Nb-Sn-HA biomaterials were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The relative density was obtained by Archimedes principle and the hardness was measured by Vickers hardness tester. The -Ti phase was obtained after 12h milling. As result of hardness and relative density, 12h milled Ti-Nb-Sn-HA composite has the highest values.

Al-42wt%Nb powder was prepared by high-energy mechanical milling(HEMM). The particle size, phase transformation and microstructure of the as-milled powder were investigated by particle size distribution (PSD) analyzer, scanning electron microscopy (SEM), X-ray diffractometery (XRD), transmission electron microscopy (TEM)and differential thermal analysis (DTA). The milled powders were heated to a sintering temperature at 1000C with under vaccum with vaccum tube furnace. Microstructural examination of sintered Ti-42wt%Nb alloy using 4h-milled powder showed Ti-rich phases (α-Ti) which are fine and homogeneously distributed in the matrix (Nb-rich phase: β-Ti). The sintered Ti-42wt%Nb alloy with milled powder showed higher hardness. The microstructure of the as quenched specimens fabricated by sintering using mixed and milled powder almost are same, but the hardness of as quenched specimen fabricated by using mixed powder increased due to solution hardening of Nb in Ti matrix. The aging effect of these specimens on microstructural change and hardening is not prominent.

Biomimetic apatite deposition behaviors on Zr-1Nb and Ti-6Al-4V plate with various surface conditions were examined. Both alloys were polished with abrasive papers to have different roughness and some of them were treated in NaOH before exposition in simulated body fluid. NaOH treatment was found to enhance the deposition rate of apatite on Ti-6Al-4V significantly. On the other hand, the deposition rate of Zr-1Nb was not influenced by NaOH treatment. Without NaOH treatment, the polished Zr-1Nb with abrasive paper was found to induce more apatite nucleation than the polished Zr-6Al-4V.