Nanostructured β-phase Ti–31.0Fe–9.0Sn and sub-μm structured Ti–39.3Nb–13.3Zr–10.7Ta alloys for biomedical applications: Microstructure benefits on the mechanical and corrosion performances

Nanostructured Ti–31.0Fe–9.0Sn and sub-micrometer structured Ti–39.3Nb–13.3Zr–10.7Ta (wt.%) β-type alloys, exhibiting different microstructures and dissimilar mechanical properties, have been prepared by copper mold casting. The microstructure, mechanical behavior and corrosion resistance, in simulated body fluid, of both alloys have been investigated and compared to those of commercial Ti–6Al–4V. Nanoindentation experiments reveal that the Ti–31.0Fe–9.0Sn rods exhibit very large hardness (H ≈ 9 GPa) and high Young's modulus. Conversely, the Ti–39.3Nb–13.3Zr–10.7Ta alloy is mechanically softer but it is interesting for biomedical application because of its rather low Young's modulus (E ≈ 71 GPa). Concerning the corrosion performance, Ti–35Nb–7Zr–5Ta shows a corrosion behavior comparable to Ti–Al6–V4, with no potential breakdown up to 0.4 V vs. Ag|AgCl. On the contrary, the Ti–31.0Fe–9.0Sn alloy exhibits a more anodic corrosion potential, but the value is still less negative than for pure elemental Fe and Ti. From all these properties and because of the absence of toxic elements in the compositions, the Ti–39.3Nb–13.3Zr–10.7Ta and Ti–31.0Fe–9.0Sn alloys are attractive for use as metallic biomaterials.     

Wear properties of Ti–13Zr–13Nb (wt.%) near β titanium alloy containing 0.5 wt.% boron in dry condition,Hank's solution and bovine serum

The effect of heat treatment on the microstructure, hardness and sliding wear behaviour of Ti–13Zr–13Nb (wt.%) containing 0.5 wt.% B (TZNB) has been studied and compared with that of Ti–13Zr–13Nb (wt.%) (TZN) alloy. The wear properties were tested in dry condition and in simulated body fluid (Hank's solution and bovine serum) to understand the effect of different medium on wear behaviour of the TZNB alloy. Depending on the heat treatment condition the microstructure of the alloy consisted of α/martensite and TiB in β matrix. In general, the hardness of all the heat treated samples varied in a narrow range and in most of the cases addition of boron to the TZN alloy decreased the hardness. Almost all cases, no significant variation of the wear rate in dry condition with heat treatment was observed. Compared with the wear rate in dry condition, the wear rate in Hank's solution of the all the TZNB samples increased substantially. Moreover, the wear was found to be most severe in bovine serum. Addition of boron to TZN alloy did not result in any improvement in the wear resistance in all the media studied.     

Microstructure and mechanical properties of 12 wt.% Cr ferritic stainless steel with Ti and Nb dual stabilization

TCS stainless steel is a 12 wt.% Cr ferritic stainless steel with 0.040 wt.% Ti and 0.096 wt.% Nb dual stabilization. This paper investigated the microstructures and mechanical properties of TCS stainless steel heated at 600–1300 °C for 10 min and followed water quenching. Results show the increasing of both tensile strength and hardness meanwhile the ductility and toughness have experienced the decreasing due to formation of martensitic phase and grain coarsening. In the unheated and heated TCS stainless steel, there are mainly two kinds of particles: Ti-rich particles in size of 2–5 μm; Nb-rich particles in size of 20–50 nm.     

Effects of grain refinement and boron treatment on electrical conductivity and mechanical properties of AA1070 aluminum

Aluminum has been used as an alternative to copper for the production of electrical grade conductors. However, good electrical conductivity with excellent mechanical properties is hard to realize. Grain refinement can improve plastic deformation and mechanical properties. Boron treatment is advantageous to the improvement of electrical conductivity. So it is promising to achieve good mechanical properties and electrical conductivity by the interaction of grain refinement and boron treatment. In our work, the effect of grain refinement and boron treatment on electrical conductivity and mechanical properties of AA1070 aluminum was studied. The ideal grain refiner is Al–5Ti–0.8B–0.2C master alloy and with 0.2% addition, the electrical conductivity keeps at 60.7% IACS. Besides, the effect of different boron additions on electrical conductivity of AA1070 aluminum was studied. With 1%Al–6B addition, its electrical conductivity can reach 64% IACS, improved by 5.3%. With 0.2%Al–6B and 0.5%Al–5Ti–0.8B–0.2C additions, the electrical conductivity can reach 63.2% IACS, ultimate tensile strength at room temperature (UTS_25 °C) is 85 MPa, and elongation (Ɛ) is 58%. Compared with AA1070 aluminum without addition, the ultimate tensile strength and elongation have been improved by 26.9% and 9.4% separately.     

Microstructure characterization of nanometer carbides heterogeneous precipitation in Ti–Nb and Ti–Nb–Mo steel

The influences of micro-alloying elements and hot deformation on the precipitation morphology of Ti–Nb and Ti–Nb–Mo steels were investigated. The nanometer sized carbide particles randomly dispersed in the ferrite matrix are attributed mainly to severe deformation at high temperature and low isothermal holding temperature. Of the two steels with different combinations of the micro-alloying elements, Ti–Nb and Ti–Nb–Mo, the steel with Ti–Nb–Mo was more effective in precipitating hardening due to its slower carbide coarsening rate. Based on observations of micrographs, the nano-sized TiMoC and TiNbC precipitated in polygonal ferrite grains when the Ti–Nb–Mo and Ti–Nb steels were isothermally treated at 650 °C for 3 min and 180 min. The smaller of the two carbides, TiMoC, precipitated in the ferrite grain, and the hardness of Ti–Nb–Mo steel was higher than that of Ti–Nb steel. Moreover, the tiny ferrite grains and high dislocation density in the Ti–Nb–Mo steel were found to provide an attractive combination of strength and toughness.     

Investigation of the effect of Al–5Ti–1B grain refiner on dry sliding wear behavior of an Al–Zn–Mg–Cu alloy formed by strain-induced melt activation process

This study was undertaken to investigate the influence of Al–5Ti–1B master alloy and modified strain-induced melt activation process on the structural characteristics, mechanical properties and dry sliding wear behavior of Al–12Zn–3Mg–2.5Cu aluminum alloy. The optimum amount of Ti containing master alloy for proper grain refining was selected as 2 wt.%. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The optimum temperature and time in strain-induced melt activation process are 575 °C and 20 min, respectively. T6 heat treatment was applied for all specimens before tensile testing. Significant improvements in mechanical properties were obtained with the addition of grain refiner combined with T6 heat treatment. After the T6 heat treatment, the average tensile strength increased from 283 MPa to 587 MPa and 252 MPa to 564 MPa for samples refined with 2 wt.% Al–5Ti–1B before and after strain-induced melt activation process, respectively. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3Mg–2.5Cu aluminum alloy to the dry sliding wear.The results showed that ultimate strength and dry sliding wear performance of globular microstructure specimens was a lower value than that of Ti-refined specimens without strain-induced melt activation process.     

Microalloying effects on microstructure and mechanical properties of 18Cr–2Mo ferritic stainless steel heavy plates

The microstructure, including grain size and precipitation, tensile strength and Charpy impact toughness of (Nb + V) 18Cr–2Mo ferritic stainless steel heavy plates with/without Ti were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and standard tensile strength and Charpy impact toughness testing. It was found that for 18Cr–2Mo heavy plate, a good combination of Nb–V stabilized method without Ti induces refinement of grain sizes due to the precipitation of amounts of fine Nb carbonitrides and V nitrides. Meanwhile, the mechanical testing results indicate that optimal transformation of grain size, precipitation that Nb–V composition system brings to 18Cr–2Mo heavy plate is beneficial to improvement of strength and impact toughness.     

Titanium–SiO2 nanocomposites and their scaffolds for dental applications

There have been a number of attempts to modify the properties of titanium implants to improve osseointegration. These modifications include alterations of the chemistry and roughness of the surface of the implant. In this work, Ti–10 wt.% SiO₂ nanocomposites and their scaffolds were synthesized using a combination of mechanical alloying and a “space-holder” sintering process. The phase and microstructure analysis was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and the properties were measured using hardness and corrosion testing equipment. An amorphous structure was obtained at 20 h of milling. The crystallization of the amorphous phase upon annealing led to the formation of a nanostructured Ti–10 wt.% SiO₂ composite with a grain size of approximately 40 nm. The Vickers hardness of the Ti–10 wt.% SiO₂ nanocomposites reached 670 HV_0.2. The in vitro cytocompatibility of these materials was evaluated and compared with conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured. The morphology of the cell cultures obtained on the bulk Ti–10 wt.% SiO₂ nanocomposite was similar to those obtained on the microcrystalline titanium. However, on the porous scaffold, the cells adhered to the insert that penetrated the porous structure with their entire surface, whereas on the polished surface, more spherical cells were observed with a smaller surface of adhesion. Porous Ti–10 wt.% SiO₂ scaffolds have been developed in order to promote bone ingrowth and to induce prosthesis stabilization.     

Microstructure development and tensile mechanical properties of Mg–Zn–RE–Zr magnesium alloy

The Mg–5.3 wt.%Zn–1.13 wt.%Nd–0.51 wt.%La–0.28 wt.%Pr–0.79 wt.%Zr alloy prepared by direct chill casting is subjected to hot extrusion. The effects of extrusion ratio and temperature on microstructure and tensile mechanical properties have been studied. The results indicate coarse grains of as-cast alloys are refined with extrusion ratio increasing from 0 to 9. The eutectic constituents are elongated along extrusion direction. However, further increase of extrusion ratio has a little influence on grain refinement and the improvement of mechanical properties of the alloy. Dynamic recrystallisation is the main mechanism of grain refinement during hot extrusion. Raising extrusion temperature results in grain coarsening. Grain shape becomes more equiaxed-like with raising extrusion temperature. At the same time, mechanical properties decrease with the increase of extrusion temperature.     

Fabrication of nano-grained Ti–Nb–Zr biomaterials using spark plasma sintering

Nanostructured near-β Ti–20Nb–13Zr at % alloy with non-toxic elements and enhanced mechanical properties has been synthesized by spark plasma sintering (SPS) of nanocrystalline powders obtained by mechanical alloying. The consolidated bulk product was characterized by density measurements and Vickers hardness (HV), and X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) combined with energy-dispersive spectroscopy (EDX), and transmission electron microscopy (TEM) for structural details. The temperature during spark plasma sintering was varied between 800 and 1200 °C, while the heating rate and holding time of 100°K/min and 10 min were maintained constant in all the experiments. The effect of SPS temperature on the densification, microstructure, and HV was discussed. The results show that a nearly full density structure was obtained after SPS at 1200 °C. The microstructure of the obtained alloy is a duplex structure with the α-Ti (hcp) region having an average size of 70–140 nm, surrounding the β-Ti (bcc) matrix. The obtained alloy was chemically homogenized with a micro hardness value, HV of 660. The developed nanostructured Ti–20Nb–13Zr alloy is suggested for biomedical use as in implant material in dental and orthopedic applications.     

Quantitative study of grain refinement in Al–Mg alloy processed by equal channel angular pressing at cryogenic temperature

Strain induced grain refinement of an Al–1 wt.% Mg alloy processed by equal channel angular pressing (ECAP) at cryogenic temperature is investigated quantitatively. The results show that both mean grain and subgrain sizes are reduced gradually with increasing ECAP pass. ECAP at cryogenic temperature increases the rate of grain refinement by promoting the fraction of high angle grain boundaries (HAGBs) and misorientation at each pass. The fraction of HAGBs and the misorientation of Al–1 wt.% Mg alloy during ECAP at cryogenic temperature increase continuously as a function of equivalent strain. Both {110} and {111} twins at ultrafine-grained size are observed firstly in Al–Mg alloy during ECAP. The analysis of grain boundaries and misorientation gradients demonstrates the grain refinement mechanism of continuous dynamic recrystallization.     

Effects of Al–5Ti–1B on the structure and hardness of a super high strength aluminum alloy produced by strain-induced melt activation process

In this study the effect of Al–5Ti–1B grain refiner on the structural characteristics and hardness of Al–12Zn–3Mg–2.5Cu aluminum alloy has been investigated. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The specimens subjected to deformation ratio of 40% (at 300 °C) and various heat treatment times (5–40 min) and temperature (550–620 °C) regimes were characterized in this study. Microstructural study was carried out on the alloy by the use of optical and scanning electron microscopy (SEM) in both unrefined and Ti-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 575 °C and 20 min respectively. The hardness test results of the alloy also revealed that T6 heat treatment is more effective in hardness enhancement of all specimens in comparison with SIMA processing.     

Effect of grain refinement on mechanical properties and sliding wear resistance of extruded Sc-free 7042 aluminum alloy

The present study deals with an investigation on dry sliding wear behavior of grain refined Sc-free 7042 aluminum alloy by using a pin-on-disc wear test machine. Al–5Ti–1B and Al–15Zr master alloys were used as grain refining agents. The optimum amounts of added Ti and Zr in the alloy were found to be 0.03 wt.% and 0.3 wt.%, respectively. Extrusion was carried out and T6 heat treatment ware applied for all rod specimens before testing. Significant improvement in mechanical properties was obtained with the addition of grain refiners. The worn surfaces were characterized by energy dispersive X-ray spectrometry microanalysis. Results showed that the wear resistance of unrefined alloy increased with the addition of both grain refiners. Furthermore, the worn surface studies showed a mixed type of wear mechanisms; delaminating, adhesive and abrasive which took place at higher applied load.     

Microstructure and notched tensile fracture of Ti–6Al–4V to Ti–4.5Al–3V–2Fe–2Mo dissimilar welds

Dissimilar welding of Ti–6Al–4V (Ti-6-4) to Ti–4.5A1–3V–2Fe–2Mo (SP-700) alloys was performed using a CO₂ laser. The microstructure and notched tensile strength (NTS) of the dissimilar welds were investigated in the as-welded and post-weld heat treatment (PWHT) conditions. Moreover, the results were compared with homogeneous laser welds with the same PWHT. The dilution of SP-700 with the Ti-6-4 alloy caused the formation of fine needle-like α + β structures, resulting in the exhibition of a moderately high fusion zone (FZ) hardness of HV 398. The high FZ hardness (HV 438) for the weld with the PWHT at 482 °C was associated with low NTS or high notch brittleness. The fracture appearance of the notched tensile specimen was related to its inherent microstructure. With increasing the PWHT temperature, the thickness of grain boundary α increased, which promoted an intergranular dimple fracture. By contrast, fine shallow dimples were present in the peak-aged weld, which was induced by the refined α + β microstructures in the basket-weave form.     

Structure and mechanical properties of as-cast Ti–5Nb–xCr alloys

As-cast Ti–5Nb and a series of Ti–5Nb–xCr with Cr content ranging from 1 to 13 mass% prepared by using a commercial arc-melting vacuum-pressure casting system were investigated. Commercially pure titanium (c.p. Ti) was used as a control. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys obviously had different structures and mechanical properties with the addition of various amounts of Cr. When 1 mass% Cr was added, the structure was comprised mainly of the α′ phase, which was also found in Ti–5Nb. With the addition of 3 mass% Cr, α′ and α′′ phases were appeared. When the Cr content was increased to 5 mass% or greater, the β phase was completely retained. Moreover, the ω phase was detected in the Ti–5Nb–5Cr and Ti–5Nb–7Cr alloys. The largest quantity of ω phase and the highest bending modulus were found in the Ti–5Nb–5Cr alloy, while the Ti–5Nb–9Cr alloy had the lowest bending modulus. Moreover, the high strength/modulus ratios of the Ti–5Nb–3Cr (22.5) and Ti–5Nb–9Cr (21.3) alloys demonstrate its advantage for use as implant materials. Also, these two alloys exhibited the better elastic recovery angles of 28.3° in Ti–5Nb–3Cr and 22.2° in Ti–5Nb–9Cr. In the current search for better implant materials, α′ + α′′ phase Ti–5Nb–3Cr and β phase Ti–5Nb–9Cr alloys with low modulus, ductile property, excellent elastic recovery capability and reasonably high-strength seem to be the most feasible alloy for orthopedic and dental applications if some other necessary properties are obtained.     

Effect of boron addition on the cavitation erosion resistance of Fe-based hardfacing alloy

The cavitation erosion behavior of Fe–Cr–C–Si–xB (x = 0, 0.3 and 0.6 wt.%) alloys were investigated up to 50 h by using 20 kHz vibratory cavitation erosion test equipment. The boron-added alloys showed the improved cavitation erosion resistance compared to the boron-free alloy. This improvement was attributed to that the boron addition enhanced the grain boundary strength and refined the grain size of the matrix. However, the cavitation erosion rate of the 0.6 wt.% boron specimen was higher than that of the 0.3 wt.% boron specimen. The higher erosion rate of the 0.6 wt.% boron was due to the larger carbide volume in the matrix.     

Microstructure and mechanical properties of in situ TiC and Nd2O3 particles reinforced Ti–4.5 wt.%Si alloy composites

(TiC + Nd₂O₃)/Ti–4.5 wt.%Si composites were in situ synthesized by a non-consumable arc-melting technology. The phases in the composites were identified by X-ray diffraction. Microstructures of the composites were observed by optical microscope and scanning electron microscope. The composite contains four phases: TiC, Nd₂O₃, Ti₅Si₃ and Ti. The TiC and Nd₂O₃ particles with dendritic and near-equiaxed shapes are well distributed in Ti–4.5 wt.%Si alloy matrix, and the fine Nd₂O₃ particles exist in the network Ti + Ti₅Si₃ eutectic cells and Ti matrix of the composites. The hardness and compressive strength of the composites are markedly higher than that of Ti–4.5 wt.%Si alloy. When the TiC content is fixed as 10 wt.% in the composites, the hardness is enhanced as the Nd₂O₃ content increases from 8 wt.% to 13 wt.%, but the compressive strength peaks at the Nd₂O₃ content of 8 wt.%.     

Laser-assisted synthesis of Ti–Mo alloys for biomedical applications

This paper presents the results of a laser-based combinatorial investigation of the Ti–Mo system, aiming at finding alloys with promising properties for orthopedic applications. Variable powder feed rate laser cladding was applied to synthesize Ti–xMo alloys with composition continuously varying in the range of 4–19 wt.% Mo. Screening was performed on the basis of the alloys' mechanical properties, in particular hardness and Young's modulus, measured by microindentation tests. Microstructural analysis showed that alloys with Mo content between 4 and 8 wt.% are composed of acicular martensite and retained β-phase, the proportion of the later phase increasing with increasing Mo content. Alloys with Mo content of 10 wt.% and higher consist entirely of β phase. All the alloys present a Mo segregation pattern indicating that solidification occurred with a cellular solid–liquid interface. Though β-phase alloys present lower values of Young's modulus and hardness than α′- or α″- containing alloys, minimum values of Young's modulus (75 GPa) and hardness (240 VHN) were achieved for the Ti–13 wt.% Mo alloy.     

Effect of impact force on Ti–10Mo alloy powder compaction by high velocity compaction technique

Ti–10Mo alloy powder were compressed by high velocity compaction (HVC) in a cylinderical form of height/diameter (h/d) in die 0.56 (sample A) and 0.8 (sample B). Compactions were conducted to determine the effect of impact force per unit area of powder filled in die for densification and mechanical properties of Ti–10Mo samples. The micro structural characterization of samples were performed by scanning electron microscope (SEM). The mechanical properties of the compressed samples such as Vickers hardness, bending strength, and tensile strength were measured. Experimental results showed that the density and mechanical properties of sample A and sample B increased gradually with an increase in impact force and decreased with an increase in height/diameter ratio. The relative green density for sample A reached up to 90.86% at impact force per unit area 1615 N mm⁻². For sample B, it reached 79.71% at impact force per unit area 1131 N mm⁻². The sintered sample A exhibited a maximum relative density of 99.14%, Vickers hardness of 387 HV, bending strength of 2090.72 MPa, and tensile strength of 749.82 MPa. Sample B revealed a maximum relative sintered density of 97.73%, Vickers hardness of 376 HV, bending strength 1259.94 MPa and tensile strength 450.25 MPa. The spring back of the samples decreased with an increase in impact force.     

Phase transformations in Ti–35Nb–7Zr–5Ta–(0.06–0.68)O alloys

The phase transformations occurring in Ti–35Nb–7Zr–5Ta–(0.06–0.68)O β solution treated and aged between 427 and 593 °C for 8 h have been investigated. Aging at 427 °C resulted, respectively, in ω, ω + α and α phase formation for 0.06, 0.46 and 0.68 wt.% O. A modification in ω phase morphology, from near circular to ellipsoidal, was also observed with increasing O from 0.06 to 0.46 wt.%.Aging at higher temperatures resulted in resolution of the ω phase in 0.06 wt.% O. Lenticular α precipitation was observed at higher O content, the volume fraction of α increasing with increasing O at a constant aging temperature and with increasing aging temperature at a constant O content. The latter also resulted in coarsening of the α precipitates and an increase in their aspect ratio. Finally aging of these alloys resulted in the formation of precipitate free zones (PFZs) along prior β grain boundaries, the width of these zones increasing with an increasing aging temperature. These observations are consistent with the ability of O to suppress ω phase formation through interruption of the 〈111〉 lattice displacement required for this phase's formation, while promoting α phase formation at higher O content, presumably through local ordering within the β phase.