Amount Of Hard Phase Research Articles

Novel Al-based Self-lubricating Wear-resistant Coatings by Low Pressure Cold Spray

To improve the wear resistance of Al coating, the Al-based self-lubricating wear-resistance coatings were fabricated by Low pressure cold spray(LPCS) technology onto Q235 carbon steel. The right amount of hard phase(Al2O3) and a lubricant(MoS2) were added to improve the wear resistance of the nonvel coating. The friction and wear behaviour were carried out using the UMT-3 fricition and wear tester by line-contact reciprocating sliding. The microstructure of coating and corresponding wear traces of these novel Al-based self-lubricating wear-resistant coatings were investigated by means of scanning electron microscopy (SEM), with the energy dispersive spectrum (EDS). The results showed that the average friction coefficient and the weight loss of the novel Al-based composite coatings with the contents of 5wt% MoS2 is lower than Al-Al2O3 composite coating. The novel Al-based composite coating showed an improved wear resistance and the wear mechanism was abrasive and adhesive wear.

Investigation on the Tribological Behavior of Arc-Sprayed and Hammer-Peened Coatings Using Tungsten Carbide Cored Wires

Due to their outstanding properties, WC-W2C iron-based cermet coatings are widely used in the field of wear protection. Regarding commonly used WC-W2C reinforced coating systems, it has been reported that their tribological behavior is mainly determined by the carbide grain size fraction. Although the manufacturing route for arc-sprayed WC-W2C cermet coatings is in an advanced state, there is still a lack of knowledge concerning the performance of cored wires with tungsten carbides as filling material and their related coating properties when post-treatment processes are used such as machine hammer peening (MHP). A major objective was to characterize WC-W2C FeCMnSi coatings, deposited with different carbide grain size fractions as a filling using cored wires, with respect to their tribological behavior. Moreover, deposits derived from cored wires with a different amount of hard phases are investigated. According to this, polished MHP surfaces are compared to as-sprayed and polished samples by means of metallographic investigations. With the use of ball-on-disk and dry rubber wheel tests, dry sliding and rolling wear effects on a microscopic level are scrutinized. It has been shown that the MHP process leads to a densification of the microstructure formation. For dry sliding experiments, the MHP coatings obtain lower wear resistances, but lower coefficients of friction than the conventional coatings. In view of abrasion tests, the MHP coatings possess an improved wear resistance. Strain hardening effects at the subsurface area were revealed by the mechanical response using nanoindentation. However, the MHP process has caused a cracking of embedded carbides, which favor breakouts, leading to advanced third-body wear.

Effect of deviatoric plastic strain on the mechanical behaviour of composite powder compacts with large amount of hard phase

The effect of increasing amounts of deviatoric plastic strain on the mechanical behaviour of powder composite compacts is investigated. The study focuses on a highly charged composite of soft Aluminium particles with hard Nickel based super-alloy particles. Three mechanical tests, imposing different stress states, are carried out at various temperatures on powder compacts that have been submitted to increasing amount of deviatoric plastic strain. These tests are used to gather information on the alterations that such deviatoric strains cause on the powder compact mechanical response. It is shown that the ductility and the yield stress of the powder compacts increase with increasing amounts of cumulated plastic strain. The particulate nature of the compact fades, but some aspects of the mechanical behaviour (macroscopic rate dependence in particular) are still characteristic of the original particulate material even after significant amount of accumulated deviatoric strain. Microstructural observations are carried out to provide a reasonable scenario for the mechanisms responsible of the alterations that deviatoric strains bring.

Effects of M‐A constituent on fracture behaviour of weld HAZs: Deterioration and improvement of HAZ toughness in 780 and 980 MPa class HSLA steels welded with high heat input (5th report)

Summary The effects of M‐A (martensite‐austenite) constituent on the initiation and propagation of cracks have been investigated by observation of the fracture morphology and cracks around the M‐A constituent. Crack initiation and propagation energies were estimated using an instrumented Charpy impact test machine. The concentration and distribution of the tensile plastic deformation introduced into the soft phase around the hard constituent were also qualitatively analysed by the finite element method (FEM) to explain the effect of the M‐A on crack initiation and propagation. The results show a sharp decrease in the crack initiation and propagation energies with increasing area fraction of the massive M‐A constituent. The FEM analysis suggests that the greater amount of hard phase reduces the crack initiation energy in the surrounding soft phase, which explains the observed decrease in the crack initiation energy with increasing area fraction of the massive M‐A constituent. It was also shown that the dec...

Effect of austenite on the properties of some wear resistant alloys

1. A change in the amount of austenite in wear-resisting alloys affects their properties. The effect depends on the structural condition of the alloy and the amount of hard phases. 2. With up to 25% hard phases (group 1 alloys) an increase in the amount of austenite raises the impact resistance. The wear resistance decreases negligibly when the amount of austenite increases to no more than 40–47%. 3. With over 33% hard phases an increase in the amount of austenite cannot improve the impact resistance, although in one case (hypereutectic alloys) an increase in the amount of austenite improves the wear resistance due to stronger gripping of the hard particles. In this case the wear resistance is highest with 15–18% austenite (3–3.5% Ni). Adding a larger amount of nickel is inexpedient, since a larger amount of austenite does not improve the wear resistance.

Friction characteristics of tungsten-boron nitride alloys

1. Materials of the tungsten-boron nitride type may prove to be quite promising for use in sliding bearings intended to operate under special conditions. We base this prediction on the high wear resistance of such materials at all the sliding speeds and pressures investigated. 2. We established the sliding speeds and pressures that produce the minimum coefficient of friction. In establishing the causes of this phenomenon, we will seek ways to further improve the friction characteristics of these materials. 3. An increase in the amount of boron nitride introduced into the powder mixture does not lead to a reduction in the coefficient of friction, apparently because of formation of a large amount of hard phases during hot pressing of the specimens.