Effect of electron beam surface melting on the microstructure and wear behavior of Stellite 12 hardfacing

PurposeThe purpose of this study is to investigate the effect of electron beam surface melting (EBSM) on the properties of Plasma Transfer Arc (PTA) deposited Stellite 12 hardfacing.Design/methodology/approachFor this purpose, structural characterization and dry sliding wear tests have been conducted on the hardfacings at room temperature. The wear tracks formed on the surfaces of the hardfacings were examined by a stylus-type profilometer and a scanning electron microscope.FindingsRefinement of the matrix and the carbides following EBSM process led to about 15 per cent increment in hardness as compared to PTA state. Despite an increase in the surface hardness, EBSM’ed hardfacing exhibited about 50 per cent lower sliding wear resistance than PTA hardfacing against alumina ball. According to the worn surface examinations, reduction in the wear resistance of Stellite 12 after EBSM process has been associated with the extensive refinement of the carbides which made them easier to be removed from the matrix during the sliding contact.Originality/valueThe authors of current study have applied EBSM to PTA deposited Stellite 12 hardfacing alloy to investigate if the surface structure and properties could be improved. More specifically the dry sliding wear performance of PTA and EBSM’ed hardfacings have been focused in the scope of this study. To the best of the authors’ knowledge, this approach, i.e. use of EBSM as a post deposition treatment of Stellite 12 hardfacings, has not been reported in open literature.

Nanotribological characteristics of laser surface melted Stellite 12+Mo hardfacing

Purpose The purpose of the study is to examine the sliding wear performance of plasma transfer arc (PTA) deposited and laser surface melted (LSM) Mo modified Stellite 12 hardfacings under high contact stresses (i.e. >20 GPa). Design/methodology/approach For this purpose, after structural characterization, sliding wear tests have been conducted using sphero-conical diamond indenter as the counterface with different normal loads. The wear tracks formed on the hardfacings were examined by atomic force microscopy and scanning electron microscopy. Findings Both hardfacings showed severe wear (at high contact stress levels ranging from 24 to 41 GPa), which progressed by plastic deformation, although the wear resistance of LSMed hardfacings was better than the PTA hardfacings by a factor of two due to its near surface microstructure characterized as carbide-rich zone. Originality/value Sliding wear characterization of a promising 10 Wt.% Mo modified version of commercial Stellite 12 hardfacings (as reported previously by authors) was done in as PTA and LSMed states using nanomechanical test system. To the best of authors’ knowledge, no report is available in the open literature on such hardfacings under these testing conditions.

Study on Corrosion Mechanism of Stellite Hard Alloy Layer of a Main Pump Component

Stellite 12 alloy was cladded on the surface of Thrust runner of a main pump using HIP technology. After product testing, lots of corrosions were found on the hard layer. SEM and EDS analysis technologies were used in order to find out the causes and mechanism inducing these corrosions. SEM results indicated that two kinds of corrosions locating on the hard layer. One type is central corrosion pit, another type is Selective Phase Corrosion (SPC).EDS showed that the central and adjacent corrosive areas were rich in carbon, low in cobalt, chromium and tungsten elements for the first type of corrosion. As for the second type of corrosion, EDS indicated that the corrosive zones were typically high in tungsten, chromium and carbon, and low in cobalt. Meanwhile, the presence of sulfur and chlorine elements may aggravate the initiation and continuation of corrosion.