Young's modulus as well as tensile strength, ductility, fatigue life, fretting fatigue life, wear properties, functionalities, etc., should be adjusted to levels that are suitable for structural biomaterials used in implants that replace hard tissue. These factors may be collectively referred to as mechanical biocompatibilities. In this paper, the following are described with regard to biomedical applications of titanium alloys: the Young's modulus, wear properties, notch fatigue strength, fatigue behaviour on relation to ageing treatment, improvement of fatigue strength, fatigue crack propagation resistance and ductility by the deformation-induced martensitic transformation of the unstable beta phase, and multifunctional deformation behaviours of titanium alloys.

Mechanical biocompatibilities of titanium alloys for biomedical applications.

https://iopscience.iop.org/article/10.1016/j.stam.2003.09.002/pdf

Recent research and development in titanium alloys for biomedical applications and healthcare goods

Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can provide good biological fixation through bone tissue ingrowth into the porous network. This paper focuses on recent developments of biomedical Ti-based alloys. It can be divided into four main sections. The first section focuses on the fundamental requirements titanium biomaterial should fulfill and its market and application prospects. This section is followed by discussing basic phases, alloying elements and mechanical properties of low modulus β-type Ti-based alloys. Thermal treatment, grain size, texture and properties in Ti-based alloys and their limitations are dicussed in the third section. Finally, the fourth section reviews the influence of microstructural configurations on mechanical properties of porous Ti-based alloys and all known methods for fabricating porous Ti-based alloys. This section also reviews prospects and challenges of porous Ti-based alloys, emphasizing their current status, future opportunities and obstacles for expanded applications. Overall, efforts have been made to reveal the latest scenario of bulk and porous Ti-based materials for biomedical applications.

/pdf/new-developments-of-ti-based-alloys-for-biomedical-1vs3nsqg8x.pdf

New Developments of Ti-Based Alloys for Biomedical Applications

Biocompatibility of β-stabilizing elements of titanium alloys

https://www.ipen.br/biblioteca/2006/11692.pdf

Corrosion characterization of titanium alloys by electrochemical techniques

Metallic materials such as stainless steel, Co–Cr alloy, pure titanium and titanium alloys have been used for surgical implant materials. The α+β type titanium alloy such as Ti-6Al-4V ELI has been most widely used as an implant material for artificial hip joint and dental implant because of its high strength and excellent corrosion resistance. Toxicity of alloying elements in conventional biomedical titanium alloys like Al and V, and the high modulus of elasticity of these alloy as compared to that of bone have been, however, pointed out [1] , [2] . New β type titanium alloys composed of non-toxic elements like Nb, Ta, Zr, Mo and Sn with lower moduli of elasticity, greater strength and greater corrosion resistance were, therefore, designed in this study. The friction wear properties of titanium alloys are, however, low as compared to those of other conventional metallic implant materials such as stainless steels and Co–Cr alloy. Tensile tests and friction wear tests in Ringer’s solution were conducted in order to investigate the mechanical properties of designed alloys. The friction wear characteristics of designed alloys and typical conventional biomedical titanium alloys were evaluated using a pin-on-disk type friction wear testing system and measuring the weight loss and width of groove of the specimen.

Corrosion wear fracture of new β type biomedical titanium alloys

This article presents the results of a study of the effects of microstructure on the fatigue strength and the short fatigue crack initiation and propagation characteristics of a biomedical α/β titanium alloy, Ti-6Al-7Nb. The results are compared to those obtained from a Ti-6Al-4V extra-low interstitial (ELI) alloy. Fatigue crack initiation occurs mainly at primary α grain boundaries in an equiaxed α structure, whereas, in a Widmanstatten α structure, initiation occurs within the α colonies and prior β grains, where α plates are inclined at around 45 deg to the stress-axis direction. In an equiaxed α structure, the short fatigue crack initiation and propagation life, where the length of the crack (a) is in a microstructurally short fatigue-crack regime (2a < 50 µm), occupies around 50 pct of the total fatigue life. On the other hand, the fatigue crack in a Widmanstatten α structure initiates at very early stages of fatigue, and, therefore, the fatigue crack-initiation life occupies a few percentages of the total fatigue life in an α structure. Then, the short fatigue crack propagates rapidly and is arrested at the grain boundaries of α colonies or prior β grains for a relatively long period, until the short crack passes through the boundaries to specimen failure. Therefore, the short fatigue crack-arrest life occupies more than 90 pct of the total fatigue life in a Widmanstatten α structure. These trends are similar between the Ti-6Al-7Nb and Ti-6Al-4V ELI alloys and biomedical α/β titanium alloys. The total fatigue life for the Ti-6Al-7Nb alloy with an equiaxed α structure is changed by the volume fraction of primary α phase and the cooling rate after solution treatment. By increasing the volume fraction of the primary α phase from 0 to 70 pct, the fatigue limit of the Ti-6Al-7Nb alloy is raised. Changing the cooling rate after solution treatment by switching from air cooling to water quenching improves the fatigue limit of the Ti-6Al-7Nb alloy significantly.

Effects of microstructure on the short fatigue crack initiation and propagation characteristics of biomedical α/β titanium alloys

Tensile properties, hardness, and Charpy impact toughness of Ti-6Al-4V extralow interstitial (ELI) with equiaxed α and Widmanstatten α structures at various stages of fatigue were investigated. Fatigue crack initiation characteristics of the same alloy were also investigated in this study. In the equiaxed α structure, fatigue cracks initiated mainly at the interface between primary-α grains, while in the Widmanstatten α structure, they initiated across α plates at an angle of around 45 deg to the stress axis. Specimens with the Widmanstatten α structure fractured before adequate fatigue hardening was achieved because a multitude of microcracks readily formed. Specimens with the equiaxed α structure fractured after adequate fatigue hardening developed. Tensile strength, 0.2 pct proof stress, and hardness increased clearly with increasing stress cycles and fatigue steps, particulary in the low-cycle fatigue (LCF) region, while impact toughness and elongation showed a reverse trend. It is suggested, therefore, that the dislocation density multiplies more rapidly near the specimen surface during the early stages of fatigue, while during the later stages of fatigue, dislocation density increases near the center of the specimen. Also, the dislocation multiplication will continue until saturation of the entire specimen has occurred.

An investigation of the effect of fatigue deformation on the residual mechanical properties of Ti-6Al-4V ELI

Long crack growth behavior of implant material Ti-5Al-2.5Fe in air and simulated body environment related to microstructure

The influence of microstructure on fracture toughness of single and duplex annealed Ti–4.5Al–3V–2Mo–2Fe alloys was investigated. For the single-annealing treatment between 1103 and 1173 K for 3.6 ks, fracture toughness, J IC , decreases first with the increase of annealing temperature from 1103 to 1123 K and then increases with increasing annealing temperature upto 1173 K. As a result, there is a minimum of fracture toughness at 1123 K. This anomalous relation between fracture toughness and annealing temperature also exists in the duplex-annealed specimens at 993 K for 3.6 ks followed by the above single-annealing treatment. Examining the change of J IC and microstructure with annealing temperature, it can be found that J IC is related to volume fraction, aspect ratio and grain size of primary α phase, width of acicular α phase and prior β grain size. The decrease of fracture toughness in the temperature range from 1103 to 1123 K is mainly due to the decrease of volume fraction of primary α phase, while the increase of fracture toughness above 1123 K is mainly caused by the increase of prior β grain size.

Kei Ichi Fukunaga

Papers

Corrosion wear fracture of new β type biomedical titanium alloys

Effects of microstructure on the short fatigue crack initiation and propagation characteristics of biomedical α/β titanium alloys

An investigation of the effect of fatigue deformation on the residual mechanical properties of Ti-6Al-4V ELI

Long crack growth behavior of implant material Ti-5Al-2.5Fe in air and simulated body environment related to microstructure

Fracture characteristics and microstructural factors in single and duplex annealed Ti-4.5Al-3V-2Mo-2Fe