Minor Additions Of Boron Research Articles

Processing and characterization of beryllium free Ni–Cr–Mo biomaterial doped with cerium, boron and titanium for dental applications

Dental restoration has been a major concern of healthcare since centuries. Several alloys are in use for dental prostheses including Ni–Cr–Mo alloy. The Ni–Cr–Mo alloy has advantage of economy and density over other alloys, while possessing equivalent corrosion and biocompatibility characteristics. However, beryllium in Ni–Cr–Mo dental casting alloys has associated health hazards, being carcinogenic. In this research Ni–Cr–Mo alloys with minor additions of boron (0.2 wt %), cerium (0.4 wt %) and titanium (2 wt %), to replace beryllium were developed through vacuum induction melting and investment casting technique. Manufacturing steps are detailed for the alloy development to have medically clean alloy, suitable for biomedical applications. The cast alloy samples were tested for microstructure, phases, melting temperatures, wear and corrosion characteristics. Corrosion and wear test results demonstrate that the composition with minor addition of cerium had a significant effect to have low corrosion rate (25.92 × 10−3 mills per year), low wear rate (0.04 × 10−4 mm3/N.m) and lowest coefficient of friction.

Boron microalloying for high-temperature eutectic high-entropy alloys

The eutectic high-entropy alloys have shown promising mechanical behaviors while their softening at elevated temperatures is still a challenge. Generally, the boundaries are the weak parts to be strengthened with increased temperatures in eutectic high-entropy alloys. Here, we found that the minor addition of boron in Ni30Co30Cr10Fe10Al18W2 eutectic high-entropy alloy can significantly strengthen the FCC grain boundaries and the FCC/B2 phase boundaries at elevated temperatures. A remarkable tensile yield strength over 581 MPa with elongation of 71 % at 800 °C is achieved with minor boron addition, corresponding to a 45 % increase in yield strength and 129 % improvement in ductility compared with the boron-free counterpart. Accompanied by the boron-strengthened phase boundary, sustainable dynamic recovery occurs in the FCC and B2 phases during high-temperature tensile testing, ensuring excellent ductility. Moreover, the benchmark test indicates that the strengthening effect of boron and borides on the boundaries contributes up to 166 MPa to the yield strength of eutectic high-entropy alloy at 800 °C. These findings shed light on the development of high-temperature eutectic high-entropy alloys with a microalloying strategy.

High Cycle Fatigue and Very High Cycle Fatigue of Orthorhombic (O + α<sub>2</sub>)-Type Ti–27.5Nb–13Al Alloy with and without B and Fatigue Striation Analysis in Comparison with (α + β)-Type Titanium Alloys

The lightweight and high strength Ti–27.5Al–13Nb intermetallic alloy, based on the orthorhombic Ti2AlNb phase (O phase) and the α2 phase incorporated, was previously developed by the authors. This alloy would seem to have good potential for applications where fatigue behavior is a main concern, such as automobile and aircraft engine parts. The minor addition of boron (B) is known to refine the ingot grain size and thus to improve the subsequent mechanical properties. For these reasons, the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of B-free and 0.1 pct B-modified Ti–27.5Al–13Nb alloy were examined in the present study. HCF tests were performed at room temperature (RT) in tension-tension mode at an R of 0.1 and a frequency of 10 Hz, while VHCF tests were performed using an ultrasonic resonance fatigue test machine at an R of −1 and a frequency of 20 kHz. In both fatigue tests, hourglass-shaped specimens were used. With the addition of 0.1 pct B, the prior B2 grain size of an ingot was reduced drastically, from 600∼1000 µm for the B-free alloy to 100∼250 µm. The 0.1 pct B-modified Ti–27.5Al–13Nb alloy with a duplex microstructure consisting of a globular α2 phase and a lamellar microstructure exhibited superior elongation of 6.1 pct at RT. The HCF curve for this alloy with a duplex microstructure was almost the same as that for a Ti–6Al–4V alloy with a fully lamellar microstructure. Although prolonged fatigue life was previously reported in the HCF region in the 0.1 pct B-modified Ti–6Al–4V alloy, the addition of 0.1 pct B to the Ti–27.5Al–13Nb, Ti–6Al–4V and Ti–4Al–2.5V–1.5Fe alloys had no such effect in the VHCF region. VHCF strength for a lamellar microstructure was ranked in the order of Ti–4Al–2.5V–1.5Fe, Ti–6Al–4V and Ti–27.5Al–13Nb from the highest. Well-defined striations were observed at the propagation stage area of the fatigue fracture surface of B-free Ti–27.5Al–13Nb, and the measured striation spacing kept a constant of 0.29 µm through the propagation distance of 300 µm. The calculation based on this observation showed that the fatigue life spent in the propagation stage was very short and thus almost 100 pct of HCF life was thought to be spent in the fatigue initiation stage. For the B-free Ti–6Al–4V alloy with an equiaxed microstructure, the striation spacing increased from 0.06 µm to 4 µm as the fatigue crack propagated for a distance of 1,000 µm. Calculation based on the striation spacing revealed that, similar to the case with the Ti–27.5Al–13Nb alloy, the fatigue initiation stage consumed almost 100 pct of fatigue life regardless of the B addition.

Microstructure and Mechanical Properties of Spark Plasma Sintered Nanocrystalline TiAl-xB Composites (0.0 <x<1.5 at.%) Containing Carbon Nanotubes

This paper investigates the effects of minor additions of carbon nanotubes (CNTs) and boron on the structure and mechanical properties of nanocrystalline TiAl intermetallic compound. Nanocrystalline TiAl-xB(0.0 < x < 1.5 at.%) composites containing 1 wt.% CNT were synthesized by mechanical alloying and spark plasma sintering. Microstructure and mechanical properties of samples were evaluated using a scanning electron microscopy, energy-dispersive x-ray spectroscopy, elemental mapping, differential scanning calorimetry, Vickers hardness measurement, and shear–punch test. The findings of the current study show that milling up to 40 h results in the formation of Ti(Al) solid solution. Further milling up to 60 h is associated with a complete amorphization of the structure. Results also show that spark plasma sintering leads to the transformation of Ti(Al) solid solution into a mixture of Ti3Al, Ti2Al, and TiAl intermetallic compounds. Minor additions of boron and CNTs cause a significant grain refinement. The addition of the latter significantly improves the elongation as well. The implications of boron/CNT additions for the microstructure of TiAl and how it correlates with the mechanical properties are thoroughly discussed in this paper.

Eutectic modification of Fe-enriched high-entropy alloys through minor addition of boron

Eutectic modification through minor addition of boron was firstly proposed to improve the malleability of brittle eutectic high-entropy alloys (EHEAs). The proposed approach involves adding small amounts of eutectic modifier, boron (0.2–1.6 at.%), to a brittle dual-phase [face centred cubic (FCC) and σ phase] Fe35Ni25Cr25Mo15 EHEA. Here, we report the role of boron additions in improvement of the mechanical properties of a Fe35Ni25Cr25Mo15 EHEA. It was found that with the increase in boron additions up to 1 at.%, the lamellar eutectic structure consisting of FCC and σ intermetallic phase gradually transited to a dendrite-like eutectic structure. As a result, the compressive fracture strain of the alloy was increased about 3 times with a slight reduction in strength. The mechanisms of eutectic morphology transition induced by boron additions in the Fe35Ni25Cr25Mo15 EHEA and their effects on mechanical properties were studied through microstructural characterization and thermodynamic analyses. The transition of eutectic morphology from lamellar eutectic to dendrite eutectic is believed to be resulted from the increased constitutional undercooling caused by B additions. The solute redistribution of B in the liquid ahead of the solid/liquid interface resulted in a B concentration gradient, which led to the formation of a constitutionally undercooled zone at the front of the σ phase, which destabilized the coupled growth conditions necessary for the formation of the lamellar eutectic structure. As a result, the eutectic morphology was transformed from lamellar eutectic to a dendritic-like eutectic structure. This type of structure exhibits a lower fraction of phase boundaries leading to improved malleability of the brittle EHEA. This insight can be used to design new advanced EHEAs through adjustment of the eutectic morphology.

Structural and electrochemical study of resorbable Ca32Mg12Zn38Yb18-xBx (x=1, 2, 3) metallic glasses in Ringer's solution

A new class of CaZn-based bulk glassy alloys with minor addition of boron and enhanced corrosion resistance for use in bioresorbable materials is introduced. The CaMgZnYbB alloys represent a new family of biomaterials with potential applications in orthopedic implants with controlled degradation rates and corrosion in the human body. The effect of substituting Yb for B in the structure on the corrosion and mechanical properties of quinternary Ca32Mg12Zn38Yb18-xBx (x = 1,2,3 at.%) alloys was investigated using X-ray diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, immersion and electrochemical polarization, compressive tests, and hardness measurements. The corrosion behavior was also evaluated using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. Microstructural investigations showed that the Ca32Mg12Zn38Yb16B2 alloy was mainly amorphous, while small reflections from nanocrystals were observed in Ca32Mg12Zn38Yb17B1 and Ca32Mg12Zn38Yb15B3. Electrochemical polarization and immersion tests in Ringer's solution at 37 °C revealed that the CaMgZnYbB alloys had significantly higher corrosion resistance than CaMgZn alloys. Electrochemical impedance spectroscopy of alloys showed only single capacitive loops. The corrosion products were identified as CaO, MgO, Mg(OH)2, and CaCO3. The compressive strengths of the alloys from 220 MPa to 283 MPa were suitable for implant applications.

Heat Treatment Study of γ + α2 Ti Aluminides Obtained through Reaction Synthesis and Hot Deformation

AbstractTi aluminides based on γ + α2 has industrial importance due to its high temperature properties coupled with low density. Processing difficulty involved in this alloy has limited its application. Alternate processing route like reaction synthesis in combination with isothermal hot working has lot of potential. Further, heat treatment of hot worked material governs the properties of the alloy. In the present paper, heat treatment of reaction synthesized plus hot worked material has been studied to obtain desirable microstructure and phases. Five alloys of Ti48Al2Cr2Nb with minor addition of boron and Ni-P coated boron is made with two different particle size of Ti powder. Homogenized and worked alloy samples are heat treated to obtain two-phase microstructure useful for high temperature application. Heat treated samples are characterized for individual phases through optical microscopy, hardness measurement and electron microscopy. An attempt has been made to study the role of boron on development of various phases and microstructure.

Structure–property correlation of a boron and carbon modified as cast β titanium alloy

Beta titanium alloys, Ti-15V-3Cr-3Al-3Sn, with minor additions of boron and carbon were prepared by consumable vacuum arc melting. Detailed microstructural characterizations were carried out using optical, scanning electron microscopes and transmission electron microscopes. Addition of boron resulted in refinement of the as cast beta grain while carbon addition resulted in the precipitation of extremely fine α phase during ageing. Formation of boride and carbide particles due to addition of boron and carbon, respectively, and refinement of the aged microstructure increased the hardness and strength as compared to the base alloy but reduced elongation to failure considerably, especially in the carbon-containing alloy where no measurable plasticity was observed. Fracture toughness values, however, were comparable for the boron- and carbon-containing alloys but these were lower than that of the base alloy.

Large-strain deformation of Ni 3Al+B: Part III. Microstructure, long-range order and mechanical properties of deformed and recrystallized Ni 3Al+B

The mechanical properties, yield-stress, hardening rate, microhardness and fracture of deformed, partially and fully recrystallized Ni 3Al, doped with minor additions of boron, were studied. The change of long range order was investigated as a function of rolling as well as of annealing temperature. At incipient stages of recrystallization, an anomalous behaviour of the mechanical properties was observed. While the yield-stress decreased, the microhardness attained a maximum. The hardness increase is attributed to thermally activated dislocation locking, while the decrease of yield-stress is interpreted in terms of the arrangement of recrystallized grains along former microbands through the sample cross-section. The intermetallic compound Ni 3Al+B can be partially disordered by cold rolling. The observed loss of long range order cannot solely be explained by the dislocation density. It is proposed that microband formation is the main cause for the measured disordering of Ni 3Al+B during cold rolling.

Large strain deformation of Ni 3Al + B: Part I. Microstructure and texture evolution during rolling

The microstructure evolution and texture development of the intermetallic compound Ni 76Al 24, doped with minor additions of boron was investigated in great detail as a function of rolling reduction at ambient temperature. The microstructure was found to become extremely inhomogeneous by formation of microbands (MB) and shear bands (SB). Dislocation cell formation was not observed. The microstructure development is interpreted in terms of forced planar slip in the L1 2 crystal structure. This causes strong work hardening and destabilizes deformation by slip while shear-band formation is promoted. The rolling texture is very weak and resembles a weak copper-type texture up to high degrees of rolling. The strongest component is the brass orientation ({110}〉112〈) after large rolling reductions; it is attributed to orientations inside shear bands. No deformation twinning was observed, even for deformation at liquid nitrogen temperature.

Large strain deformation of Ni 3Al+B: Part II. Microstructure and texture evolution during recrystallization

The microstructure evolution and texture development of the intermetallic compound Ni 76Al 24, doped with minor additions of boron, was investigated during annealing subsequent to cold-rolling. Upon annealing of cold-rolled specimens, a hardness increase prior to recrystallization was observed. This is attributed to a relaxation process of the dislocation cores during annealing. Recrystallization proceeded with very different kinetics locally and a very small recrystallized grain size was obtained. From grain growth kinetics, the activation energy for grain boundary motion was found to be close to the activation energy for self-diffusion of Ni in Ni 3Al. The recrystallization texture was almost random. However, three texture components could be invariably recognized ({013}〈100〉, {012}〈021〉 and {112}〈294〉). They are related by special orientation relationships to the brass rolling orientation. A high frequency of annealing twins occurred in the recrystallized microstructure. The misorientation distribution function (MODF) shows a preference of certain low Σ boundaries, namely small-angle boundaries (Σ1) and twins (Σ3).

Microstructure and Textures in Rolled and Recrystallized Ni3Al + B

The deformation and recrystallization structure as well as the evolution of crystallographic textures of heavily deformed, partially and fully recrystallized Ni 3 Al, ductilized with minor additions of boron, were investigated. The macroscopic orientation distribution was determined by X-ray pole-figure measurements and subsequent computation of the orientation distribution function (ODF). Convergent electron beam diffraction (CEBD) was employed to obtain information on the orientation topography and the orientation relationship of volume fractions adjacent to deformation inhomogeneities. Single grain orientation measurements by electron back scattering patterns (EBSP) were carried out to study the orientation distribution of new grains in the recrystallized microstructure. From this data the micro texture and the misorientation distribution function were calculated and the grain boundary character distribution was analysed. The results are discussed with regard to the mechanisms which govern the evolution of the conspicuously inhomogeneous deformation microstructure and deformation textures. A model for the interpretation of the observed microstructure and texture evolution is proposed.