Wear Behavior of Conventionally and Directly Aged Maraging 18Ni-300 Steel Produced by Laser Powder Bed Fusion

This study aims to explore the wear performance of maraging 18Ni-300 steel, fabricated via laser powder bed fusion (LPBF). The building direction dependence of wear resistance was investigated with various wear loads and in terms of ball-on-disk wear tests. The effect of direct aging heat treatment, i.e. aging without solution heat treatment, on the wear performance was investigated by comparing the wear rates of directly aged samples, followed by solution heat treatment. The effect of counterpart material on the wear performance of the maraging steel was studied using two counterpart materials of bearing steel and ZrO2 balls. When the bearing steel ball was used as the counterpart material, both the as-built and heat-treated maraging steel produced by the LPBF showed pronounced building direction dependence on their wear performance when the applied wear load was sufficiently high. However, when the ZrO2 ball was used as the counterpart material, isotropic wear resistance was reported. The maraging steel produced by the LPBF demonstrated excellent wear resistance, particularly when it was aging heat-treated and the counterpart material was ZrO2. The directly aged sample showed wear performance almost the same as the sample solution heat-treated and then aged, indicating that direct aging can be used as an alternative post heat treatment for tribological applications of the maraging steels produced by LPBF.

Formation of Tribofilm in the Friction of Fluorinated Diamond-Like Carbon (FDLC) Film against Ti6Al4V in Bovine Serum Albumin (BSA) Solution

A route to reducing the wear of the metal counterpart in the friction of meatal against diamond-like carbon (DLC) is to form a lubricating tribofilm on the metal counterface. However, in liquid lubricating conditions, the formation of tribofilm can be influenced by both the lubricating medium and the counterpart material. Here we report the effect of lubricating biomolecule and doping fluorine element on the formation of tribofilm in fluorinated DLC (FDLC)-Ti6Al4V friction system. A group of ball-on-disc frictional experiments with different sliding speeds and normal loads were performed in phosphate buffer solution (PBS) and bovine serum albumin (BSA) solution. The results showed the formation of tribofilm was inhibited by the absorption of biomolecules on the frictional surface, thus improving the friction coefficient and wear of Ti6Al4V counterpart. Doping fluorine into DLC film also can restrain the formation of tribofilm on Ti6Al4V counterface. As a result, tribofilm is difficult to form when Ti6Al4V counterface slides against FDLC in BSA solution. Fluorinated DLC film should be considered carefully for the anti-wear use in body fluid containing biomolecules because it might cause severe wear of the counterpart material.

Comparative study of nitrogen implantation effect on mechanical and tribological properties of Ti-6Al-4V and Ti-10Zr-10Nb-5Ta alloys

The effect of nitrogen implantation on mechanical and tribological properties of Ti-6Al-4V and Ti-10Zr-10Nb-5Ta alloys was studied. Increasing implantation dose from 1 × 1016 N+/cm2 to 2 × 1017 N+/cm2 leads to increase gradually both hardness and Young's modulus. The results show that implantation of 2 × 1017 N+/cm2 allowed to double the value of Young's modulus and to triple the value of hardness. Friction tests that have been conducted against 100Cr6 steel and alumina balls showed that tribological behavior of the two alloys depend on the nature of the counterpart material and is strongly affected by the implanted dose of nitrogen.

Tribological and Mechanical Properties of Materials for Friction Pairs Used to Space Docking

The microstructures and tribological properties of materials for friction pairs used to space docking were investigated by optical metallographic microscope and a special home-made tribo-tester, respectively. The results demonstrate that friction material appears homogeneous and compact microstructure. Counterpart material presents temper sorbite which keeps martensite morphology and residues a small amount of blocky undissolved ferrite; the porosity of friction material is about 3.7%. Materials for space docking show favorable rigidity; during running-in, friction torque of friction pairs can be enhanced obviously; under different operation conditions, friction pairs for space docking possesses different friction coefficient.