Sliding wear behaviour of steel carburized using Na 2

Experiments have been carried out to investigate the effect of carburization process on the sliding wear resistance of mild steel. The carburization process was conducted in carbonate salts mixtures of Na2CO3-NaCl. Carburization followed by water quenching resulted in the formation of martensite with a hardness of 900 HV in the subsurface, up to the depth of 400 μm. This hardness value was substantially higher than the non-carburized steel which had a hardness of 520 HV. In the initial stage of sliding in air, abrasive wear and cluster of fine cavities due to adhesion were formed. This was followed by the formation of large-scale fracture at the cavities. The high hardness of the carburized steel reduced the severity of adhesive wear and thus the tendency of the worn surface to fracture

Effects of deep cryogenic treatment on friction and wear of EN24 steel against alumina under dry and lubrication conditions

As-received (AsRec) EN24 steel was treated with conventional heat treatment (ConHeatTreat) without tempering followed by deep cryogenic treatment (DeepCryoTreat) as a supplemental treatment to study its tribological behaviour against alumina without or with mineral oil (MO) under different normal loads of 1 N and 5 N. The ConHeatTreat of the AsRec-EN24 obtained an 218.5% improvement in its hardness as the supplemental DeepCryoTreat of the ConHeatTreat-EN24 resulted in a 11.7% further improvement in its hardness. As a result, the ConHeatTreat-EN24 had the 67.5% and 56.3% lower wear volumes for 1 N and 5 N under dry condition and the 53.6% lower wear volume for 5 N under MO lubrication condition compared to those of the AsRec-EN24, respectively. The DeepCryoTreat-EN24 had the 11.5% and 39.7% lower wear volumes for 1 N and 5 N under dry condition and the unmeasurable wear volume for 5 N under MO lubrication condition compared to those of the ConHeatTreat-EN24, respectively. It could be concluded that the supplemental DeepCryoTreat further improved the hardness and thereby the abrasive wear resistance of the ConHeatTreat-EN24 under both dry and lubrication conditions.Published versio

Formation and Characterization of Nanolayered Pd-Based Metal/p-4H SiC Systems with Ohmic Behaviour

Three types of nanolayered Pd-based metal/p-4H SiC systems, Au/Pd, Au/Pd/Al and Au/Pd/Ti/Pd have been investigated and compared to Pd monolayered metallization regarding the electrical and thermal properties. The lowest contact resistivity of 2.8x10-5 .cm2 has been achieved with the Au/Pd/Ti/Pd contact. This contact exhibits excellent thermal stability during long-term heating at temperature of 700oC and at operating temperatures up to 450oC. The surface morphology investigation has shown that despite the observed decrease, the palladium agglomeration has been not avoided completely in the same contact. The dominated surface roughness was measured to be 75 nm. However, the formation of dendrites in certain places leads to increase the surface roughness to 125 nm. The structural analysis revealed that palladium silicides are formed at the interface metal/p-4H SiC which affects on decrease of the barrier height in more than two times and conversion of the contact from Schottky into ohmic.</jats:p

Evolution of compressive strains in retained austenite during sub-zero Celsius martensite formation and tempering

The development of martensite during sub-zero Celsius treatment of a 1 wt.% C, 1.6 wt.% Cr steel was investigated by in situ and ex situ (synchrotron) X-ray diffraction at the synchrotron facility HZB-BESSY II in order: (i) to quantitatively assess the fractions of retained austenite and martensite; (ii) to measure the evolution of the lattice strain in retained austenite; and (iii) to identify the different stages of tempering. This work shows for the first time that the compressive strains built up in austenite upon martensite formation during sub-zero Celsius treatment are retained after tempering. Furthermore, it is demonstrated that sub-zero Celsius treatment after tempering leads to compressive strain in austenite. Finally, it is reported that no compressive strain builds up in austenite when the martensite formation occurs below a certain critical temperature