The edge effect of specimens in abrasive wear testing

In abrasive wear testing, the specimen edges may exhibit increased wear rates. To determine the extent of edge wear, a series of tests was conducted with the crushing pin-on-disk device. The test pin was divided into two sections, separating the wear area into inner and outer pin areas. The tests were conducted with granite and quartz rocks of varying size. The edge effect was determined as the difference of the mass loss of a specimen comprising both the inner and outer parts and the mass loss of the inner part alone scaled to the size of the combined pin area, representing a specimen without edge wear. The tests showed increased edge effect with larger rocks, depending on the mechanical strength of the abrasive material. When using only large rocks with good mechanical strength, the edge effect could be as high as 50 % of the total specimen mass loss, whereas with more fragile rocks of smaller size, the edge effect was close to 0 %

Leaded tin bronzes: the effects of casting method on dry sliding behaviour

In metal-to-metal sliding bearing applications, leaded tin bronzes are widely known as materials with excellent seizure resistance. In conditions of boundary or dry lubrication, lead may smear across the sliding surface, preventing surface contact and catastrophic seizure. The aim of this study was to determine the effects of casting method on the dry sliding behaviour of leaded tin bronzes. Continuous cast, centrifugally cast, and sand cast leaded tin bronze samples with varying lead contents were subjected to pin-on-disk- testing. It was found that casting method has a significant effect on the wear behaviour of leaded tin bronzes in dry sliding conditions. With continuous cast samples, the dominant wear mode was rapid, stable microcracking along copper/lead interfacial boundaries. With centrifugally and sand cast samples, wear occurred more slowly and erratically through the formation of transfer layers. The dominant wear mode was found to be connected to the coarseness of the distribution of lead particles in the copper matrix

Development of a test device for the evaluation of journal bearings

Journal and thrust bearings are widely used in heavy industry. Today, there is a growing need for studying different kinds of new bearing material and coating solutions in operating conditions where full film lubrication cannot be achieved or sustained. A test device for the evaluation of journal bearings was developed. The device consists of a rotating shaft and four stationary test bearings. This scheme eliminates the need for support bearings, allowing an accurate measurement of friction. The initial tests were carried out with a variety of loads and sliding speeds in mixed and full film regimes. The friction results in the form of a Stribeck curve were obtained and found to be in line with general trends. The results also indicate that the bearing lift-off speed occurs when the value of the non-dimensional ηen / ppro - parameter is in the range of 0.5·10-8 - 1.0·10-8

Erosion-oxidation of pressure vessel steel P265GH

The behaviour of pressure vessel steel P265GH was studied in a centrifugal high-temperature erosion apparatus under impacts by silica (SiO2) particles moving at velocities ranging from 20 to 60 m s-1 and contacting the surface at the angles of 30° and 90°. Besides particle impacts, the steel was simultaneously exposed to air and elevated temperatures of 350 and 450°C. For comparison, the tests were also performed in the absence of erodent particles. After the tests, the material behaviour was evaluated in terms of occurred weight changes and surface characteristics, the latter ones of which were investigated by using, for example, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In the analysis of the test results, special attention was paid to the composition and microstructure of the used silica particles and how these influence the elemental distribution on the exposed surfaces. The results show that the particle impacts introduce weight losses that follow a ductile angle-dependency, i.e., relatively greater weight losses at the shallow than at the steep impact angle. Although evident oxide scales developed on the surfaces at the test temperatures, they did not provide the steel with protection against particle impacts. Particle debris was detected embedded in the surfaces particularly under impacts at 90°, with softer particle constituents being preferentially deposited. These results are discussed in terms of the erosion-oxidation behaviour of the steel and the consequences of the heterogeneous erodent particle quality

Role of fracture toughness in impact-abrasion wear.

Two new low alloyed steels were developed with different fracture toughness values but at similar level of hardness with same composition and microstructural phase. The steels were subjected to impact-abrasion wear test. This work examines specifically the additional role of toughness during impact-abrasion wear, using a newly developed high toughness steel. Microstructural characterisation of the damaged samples revealed that better toughness helps resist both impact and abrasion damage.Tata Steel Indi

Crystallography, morphology, and martensite transformation of prior austenite in intercritically annealed high-aluminum steel

The crystallography and morphology of the intercritical austenite phase in two high-aluminum steels annealed at 850 °C were examined on the basis of electron backscattered diffraction analysis, in concert with a novel orientation relationship determination and prior austenite reconstruction algorithm. The formed intercritical austenite predominantly shared a Kurdjumov–Sachs-type semicoherent boundary with at least one of the neighboring intercritical ferrite grains. If the austenite had nucleated at high-energy sites (such as a grain corner or edge), no orientation relationship was usually observed. The growth rate of the austenite grains was observed to be slow, causing phase inequilibrium even after extended annealing times. The small austenite grain size and phase fraction were consequently shown to affect martensite start temperature. Both steels had distinct variant pairing tendencies under the intercritically annealed condition.acceptedVersionPeer reviewe

High temperature high strain rate testing with a compressive SHPB

Both temperature and strain rate have a significant effect on the mechanical behavior of most materials. At or close to room temperature, well-designed and well-built SHPB devices can be used to produce high quality high strain rate data relatively easily, but at elevated temperatures many practical difficulties make such tests much more complicated. There is, however, an increasing interest and practical need to study and model the high strain rate behavior of materials also at high temperatures, and therefore development of sophisticated high strain rate high temperature testing devices is needed. In this paper, a fully computer controlled Split Hopkinson Pressure Bar (SHPB) testing system with a high température capability up to 1000°C is described The high température (HT) system is based on fast pneumatic specimen and pressure bar manipulation devices which en able heating up of the specimen only and limit the contact time of the hot specimen with cold pressure bars to 50...100 ms Some results of the tests made with the new HT-SHPB device are also presented in this paper

Microstructure and texture evolution in high manganese TWIP steels

The mechanical behavior of high manganese TWIP (Twinning Induced Plasticity) steels is characterized by a combination of good formability and high strength. The exceptional work hardening capability of TWIP steels is generally attributed to the gradually proceeding twinning of crystal planes during deformation, forming strong obstacles to dislocation motion. The onset of twinning depends on the orientation of the individual grains with respect to the loading direction and is therefore texture sensitive. In order to get better insight into the active deformation mechanisms resulting in the typical mechanical behavior of fully austenitic TWIP steels, a hot rolled Fe-28wt.%Mn-1.6wt.%Al-0.3wt.%Si-0.08wt.%C TWIP steel was studied by means of electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) after the specimens had been uniaxially deformed to different degrees of plastic deformation. Lowering the deformation temperature to −50°C resulted in increased strength values and decreased elongation values due to premature twinning and at the same time incomplete texture evolution. An increase in strain rate gave rise to extensive twinning and resulted in increased strength values. In addition to the rather coarse grained grade, a fine grained grade was produced via a recrystallization procedure with the objective to study the effect of grain size on the extent of twinning