Potential use of Friction Welding for Fabricating Semi-Biodegradable Bone Screws

Abstract

Certain surgical interventions, such as fractures, may require implants that have a combination of external and internal parts made of inert and biodegradable biomaterials, respectively. This implant design can be fabricated using specific fabrication methods such as friction welding that are able to efficiently combine two biomaterials. This study reports the utilization of the direct friction welding technique for the fabrication of semi-biodegradable bone screws using two parent metals of low carbon steel and austenitic stainless steel 202. The welding parameters were optimized to obtain welded joints for bone screw fabrication. The mechanical properties of metals that have been welded were identified through tensile and three-point bending analyses. The corrosion test was then conducted on the welded metals through the measurement of corrosion rate, changes in pH value, morphology visualization, and element release, while the cytotoxicity effect was evaluated through a cell viability test. Screw implant materials with a diameter of up to 12.7 mm were successfully fabricated using a continuous friction drive welding machine at 4000 rpm and 24.5 MPa hydraulic pressure. The results of mechanical testing show that the tensile strength of weld joints decreased by 3.6% from low carbon steel and 20.4% from stainless steel. Fractures were observed at the welding interface after being subjected to flexural testing. The pH value of the Saline solution decreased from 7.13±0.06 to 6.73±0.06 after the welded metals were immersed for up to 8 weeks. Evaluation of the surface morphology in all welding zones at week eight samples obtained that almost all types of corrosion that occurred were uniform corrosion, except in the PZ zone where galvanic corrosion was formed. The concentrations of Cr and Ni ions (ppm level) were very low, namely 0.058 ppm for Cr and 0.199 ppm for Ni. The viability of human fibroblast cells was maintained at higher than 75% viability after the cell incubation at 1, 3, and 5 days with different parts of welded joints.

Thermal–Mechanical and Microstructural Simulation of Rotary Friction Welding Processes by Using Finite Element Method

“…According to relation (10), there is a direct relationship between the grain size and the Zener-Hollomon parameter. Additionally, relation (9) states that an increasing temperature will cause the Zener-Hollomon parameter to decrease exponentially. As a result, there is an inverse relationship between temperature and the recrystallized grain size in each region, as the grain size was calculated to be in the vicinity of the weld interface, where the temperature is the highest.…”

“…On the right side, the hydraulic unit, clamp, and movable jack work in unison to exert a consistent pressure on the other sample. This intricate setup ensures the effective operation of the rotary friction welding process [9]. With the advancement of manufacturing technologies and the increasing demand for cost-efficiency, numerical methods are increasingly being utilized by researchers to study the RFW process.…”

Tensile Strength and Microstructure of Rotary Friction-Welded Carbon Steel and Stainless Steel Joints

“…When welding a harder material (i.e., medium-carbon steel) with 304 SS, careful control of the friction pressure was required, whereas welding low-carbon steel, as the softer material, required more consideration of the friction time variation. This phenomenon could be explained by the suggestion that the friction time was required to bring the material to its peak temperature [21]. As a result, a sufficient friction time was required to heat up the softer materials.…”

“…It has been applied in the petrochemical and power generation industries [20]. For medical applications, the materials have been combined to produce semi-biodegradable bone screws [21]. In the construction sector, a combination of carbon steel and stainless steel was used in the construction of concrete structures in a marine environment [22].…”

“…A certain combination of heating pressure, upset pressure, and heating time was suggested to achieve the best tensile strength in RFW 304 SS with 316 stainless steel [29]. The parameter combinations of the rotating speed, friction pressure, forging pressure, and friction time for achieving the maximum tensile strength were found in the RFW of low-carbon steel and 202 stainless steel, which were used for semi-biodegradable bone screws [21].…”