Electrochemical behavior of Ti/Al2O3 interfaces produced by diffusion bonding

Abstract

In the field of biomedical applications a special interest exists regarding the study of the physicochemical and mechanical behaviour of materials, with special focus on the electrochemical degradation of metal/ceramic interfaces. In fact, metal/ceramic interfaces may be present in several biomedical devices, ranging from external or implantable sensors, to dental implants. Diffusion bonding represents an important technique since, in opposition to other production technologies, such as active metal brazing, avoid the possible liberation of certain chemical components harmful to health. The aim of this work is to study the electrochemical degradation of the interface formed between commercially pure Ti and Al2O3 produced by diffusion bonding, in contact with a physiological solution. The present approach included the evaluation of the contribution of individual and pairs of interfacial layers on the global degradation processes. For this propose d.c. electrochemical techniques were used to monitor the open-circuit potential, and to perform potentiodynamic polarization and galvanic corrosion evaluation. Also, electrochemical impedance spectroscopy was used as a complementary technique of the corrosion behaviour of the interface. Chemical composition and morphology of samples and corrosion products were evaluated by SEM and EDS analysis. According to experimental results, two principal reaction layers were formed in the interface: TiAl and Ti3Al. The TiAl layer appears to be the responsible for the strong increase in corrosion rate of the interface

Calcium orthophosphates

“…To the best of my knowledge, Hanks’ balanced salt solution (HBSS) 857 was the first successful simulating medium containing the ions of calcium and orthophosphate together with other inorganic ions and glucose. HBSS is commercially available and still used in biomimetic experiments; 858 - 860 its chemical composition might be taken, e.g., from references 861 and 862. Other popular physiological solutions include α-modified Eagle’s [l] medium (α-MEM) and its variation, Dulbecco’s [m] modified Eagle’s medium (DMEM), which contain numerous bioorganic (alanine, aspartic acid, glycine, biotin, vitamin C, folic acid, riboflavin) and inorganic (CaCl 2 , KCl, NaCl, NaH 2 PO 4 ) components, 863 - 867 phosphate buffered saline (PBS) that contains only inorganic (CaCl 2 , MgCl 2 , KCl, KH 2 PO 4 , NaCl, NaH 2 PO 4 ) components 868 , 869 .…”

Recent Progress in the Joining of Titanium Alloys to Ceramics

“…As mentioned, when titanium is added to the brazing alloys, the diffusion is accelerated, which promotes the formation of strong reaction layers with a beneficial effect on the mechanical behavior of the joints. For this reason, some of the published works [43][44][45][46][47] are dedicated to the development of diffusion bonding between pure titanium and ceramics such as alumina and zirconia. Despite being a less appealing bonding process due to economic issues, some researchers have devoted attention to the development of the diffusion bonding process to obtain sound joints with appreciable mechanical properties.…”

“…The bonding is ensured by the formation of a reaction layer composed of equiaxed grains of Ti3Al that can be observed in the transmission electron microscopy (TEM) image of Figure 17. Rocha et al [45] also studied the interfaces of Ti/Al2O3 joints produced by diffusion bonding. Diffusion bonding experiments were performed at 800 °C for 90 min under a pressure of 5 MPa.…”

“…The successful application of these advanced ceramics depends strongly on the joining of these materials with metals. In addition, the possibility to combine properties as high wear resistance and high thermal stability with low density, high temperature properties, and excellent creep and corrosion resistance could enable the production of more advanced components that better meet the high requirements of several industrial sectors [21].The most suitable methods for bonding metals and ceramics and producing successful joints with appreciated properties are brazing , diffusion bonding [43][44][45][46][47][48][49][50][51][52][53][54][55] and transient liquid phase bonding [56,57]. All these processes present advantages and disadvantages in dissimilar joining between titanium alloys and ceramics and its selection will depend on the application.…”

Preparation of spherical calcium phosphate granulates suitable for the biofunctionalization of active brazed titanium alloy coatings

“…Direct ceramic-metal bonding has thereby been limited to metallurgical processes. Diffusion bonding, for example, has been proposed as a way to join titanium to alumina for biomedical applications [17,26]. However, close-fitting of titaniumbased linings onto ceramic prosthesis remains the standard used in the biomedical field.…”