Tribological performance and corrosion behavior of CoCrMo alloy

The present work focuses on the Tribological properties and corrosion behavior evaluation of sintered CoCrMo alloy. The CoCrMo alloy was elaborated by Powder metallurgy process at various sintering temperatures (1200°C, 1250°C and 1300°C). The structural properties were characterized by X-ray diffraction and scanning electron microscopy. The tribological characteristics were measured using a dry disc-ball tribometer. The corrosion behavior of the samples was studied using different electrochemical tests in a simulated physiological environment (Hank’s solution). The obtained results show that higher sintering temperatures have a positive impact on the tribological behavior as well as the corrosion resistance of CoCrMo alloys. The sintered samples at 1300°C showed a better resistance to friction wear and a lower corrosion rate.

COMPARISON OF THE CORROSION PROPERTIES OF CoCrMo DENTAL ALLOYS IN ARTIFICIAL SALIVA

CoCrMo alloys are known for their biocompatible properties, which, together with their favorable mechanical properties, mean they can be efficiently used in dentistry. With the development of selective laser melting for the fabrication of 3D printed objects, interest in the corrosion properties of this alloy has risen in the field of prosthodontics. In the study, CoCrMoW dental alloys were studied in artificial saliva at body temperature i.e. 37 °C. Different forms of CoCrMoW alloy were selected: a reference sample, i.e. original material as-received from the supplier, a casted sample acquired from an ordinary procedure in a dental laboratory, and two 3D printed samples made from CoCrMoW powder using the selective laser melting method (SLM). Electrochemical, spectroscopic and hardness measurements were conducted. It was shown that the reference and cast samples have similar microstructural and electrochemical properties, while the electrochemical properties of the 3D printed samples differ, most probably due to the effect of the higher micro porosity and chemical composition of the alloys.

Microstructural Characterization of Borided Co-Cr-Mo Alloy

This study involves the effect of boriding powder composition on the microstructure and hardness of a CoCrMo alloy borided in a solid medium using the powder pack method. To investigate the effect of boriding powder composition, two different commercial boriding agents, Ekabor-HM and Ekabor III, were thoroughly mixed with ferrosilicon powders to form the boriding media. The CoCrMo samples were tightly packed with the Ekabor-HM and Ekabor III boriding powders in stainless steel containers to minimize oxidation. The boriding process was carried out under atmospheric conditions for 9 h in an electrical resistance furnace preheated to 1223 K. X-ray diffraction (XRD) analyses revealed that the surfaces of the borided CoCrMo alloys consisted of a bilayer composed of CoB and Co2B phases and also contained minor amounts of CrB, Mo2B5, and Mo2B. The average thickness of the boride layer in the samples borided with Ekabor HM and Ekabor III powders was 28±4.1 μm and 21±2.3 μm, while the average hardness of the boride layer was 1752±5.3 HV0.1 and 1364±3.8 HV0.1, respectively.

The Effect of Protein Structure and Concentration on Tribocorrosion and Film Formation on CoCrMo Alloys

The formation of tribochemical reaction layers, better known as tribofilms, on cobalt-chromium-molybdenum (CoCrMo) alloys commonly used in orthopaedic applications has been hypothesized to reduce degradation owing to wear and corrosion. However, the mechanisms and pathways influencing tribofilm formation remain largely unknown. This study aims to develop a clearer understanding of the role of protein structures and its concentration on tribocorrosion and surface tribofilms formed on CoCrMo alloys during boundary regime sliding. A reciprocating tribometer with a three-electrode electrochemical cell was employed to simulate and monitor the tribocorrosion of CoCrMo in situ. As-received Foetal Bovine Serum (as-FBS) and pre-heated FBS at 70 °C for 1 h (de-FBS) were diluted with saline (0.9% NaCl) at different concentrations (25% and 75% v/v) and utilized as electrolytes during the tribocorrosion tests. The result shows that the denatured protein structure in electrolyte tends to reduce the volume losses due to wear and corrosion on the CoCrMo samples with an appreciation of the protein tribofilms. On the other hand, an increased protein concentration increased the total volume loss due to corrosive processes. A novel finding revealed in this study is that the tribocorrosion mechanism of the CoCrMo surface is dependent on the protein structure, concentration and sliding duration due to the change in surface condition.

Recent Developments in Coatings for Orthopedic Metallic Implants

Titanium, stainless steel, and CoCrMo alloys are the most widely used biomaterials for orthopedic applications. The most common causes of orthopedic implant failure after implantation are infections, inflammatory response, least corrosion resistance, mismatch in elastic modulus, stress shielding, and excessive wear. To address the problems associated with implant materials, different modifications related to design, materials, and surface have been developed. Among the different methods, coating is an effective method to improve the performance of implant materials. In this article, a comprehensive review of recent studies has been carried out to summarize the impact of coating materials on metallic implants. The antibacterial characteristics, biodegradability, biocompatibility, corrosion behavior, and mechanical properties for performance evaluation are briefly summarized. Different effective coating techniques, coating materials, and additives have been summarized. The results are useful to produce the coating with optimized properties.

Tribological Performance of CoCrMo Alloys with Boron Additions in As-Cast and Heat-Treated Conditions

The present study evaluates the effect of boron additions on the tribological performance of CoCrMo alloys. The alloys were prepared with boron ranging from 0.06 to 1 wt%. The materials were characterized using metallographic techniques, scanning electronic microscopy, and roughness and hardness tests. Tribological evaluation was made by means of ball-on-disc tests for sliding distances of 4, 8 and 12 km. The samples were in the as-cast condition and after a heat treatment at 1200 °C for 1 h, finished by water quenching. The results showed that wear resistance was influenced by the microstructure and the number of secondary phases. The volume loss decreased as the boron content increased. Due to hard phases, abrasion wear was observed. Delamination fatigue was also detected after long sliding distances. Both wear mechanisms diminished in higher boron content alloys.

Effect of Cu on the Tribocorrosion Behavior of Antibacterial CoCrMo Alloys in Simulated Biological Environment

CoCrMo alloy containing copper element can significantly improve the antibacterial property of the alloy. However, most metal implants often fail due to the presence of corrosion and wear. In this work, the electrochemical and tribocorrosion properties of CoCrMo, CoCrMo–2Cu, and CoCrMo–4Cu alloys at a potential of −0.45 V and 0 V condition in Hank’s/Saliva/α-minimum essential medium (MEM) containing 10% FBS solutions were studied to reveal the effect of Cu addition on the tribocorrosion properties of Co-based alloys. The results showed that the addition of copper element reduced the corrosion resistance and wear resistance of Co-based alloy. As for solutions, α-MEM containing 10% fetal bovine serum shows lubrication function. Based on the calculated results, it was pointed out that the tribocorrosion behavior of CoCrMo and CoCrMo–Cu alloy was mainly controlled by the mechanical wear.