Subsurface Deformation Zone Research Articles

Exploring the potential of coal derived graphite as next generation lubricant additive for multifunctional applications

In the present study, the friction and wear characteristics of steel/steel contact under reciprocating sliding conditions were investigated using composite mixtures made from Polyalphaolefin 4 (PAO4) as base oil lubricant and North Dakota lignite-derived graphite (LG) as high-value carbon additive. The results show that addition of 1 wt% LG to PAO4 led to a reduction in the friction coefficient and wear volume by ∼15 % and ∼13 %, respectively. In addition, the oxidation induction time (OIT) at 160 °C was increased by ∼29 %, which further indicates good stability of the formulated composite lubricant against oxidative degradation. The primary wear mechanism on AISI 52100 steel flat and counter-body was found to be abrasive wear under high-contact stress reciprocating sliding conditions, where tribo-oxide films of 100–200 nm were observed on the wear tracks of 52100 steel surfaces using focused ion beam scanning transmission electron microscopy (FIB-STEM). Furthermore, cross-sectional analysis of the wear track of AISI 52100 steel revealed that 1 wt% of LG additive reduced the thickness of the sub-surface deformation zone by 44 %, which indicates higher load-bearing capacity and improved wear resistance.

Corrosion Behaviour of Ni-Based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850°C

As a newly developed technology, oxyfuel combustion makes CO2 capture and sequestration feasible but raises a corrosion problem because of high concentrations of CO2 in flue gases at high temperatures. Conventional ferritic/martensitic heat resisting steels are sufficient to resist corrosion in oxygen or air but cannot survive in CO2-rich gases. To increase the process efficiency, higher temperatures will be used for energy production. As a result, austenitic steels and/or nickel-base alloys are required because of their superior corrosion resistance and mechanical properties at high temperature. This paper investigated the corrosion behavior of three nickel-based chromia-forming commercial alloys (230, 617 and 601) at 750°C and 850°C in a carbon dioxide environment for up to 500 h.Samples were cut to form 10mm x 8mm x (0.8-3) mm rectangular shaped coupons. After cutting, all surfaces of samples were ground up to 1200-grit finish, and further polished down to 3μm. Electro-polishing in 15% concentrated hydrochloric acid was used to remove the subsurface deformation zone. The grain sizes of 617 are larger (100-200μm) than those of 230 (20-80μm) alloy, and the 601 (10-30μm) alloy has the smallest grain size. All samples were ultrasonically cleaned with ethanol before being reacted in Ar-20%CO2 at 750℃ and 850°C, for up to 500 h. After reaction, samples were analysed by surface X-ray diffraction, metallographic cross-section analysis by optical microscopy, and scanning electron microscopy together with energy dispersive X-ray analysis.All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight changes. Internal Al2O3 was precipitated beneath a thin protective chromia layer for all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were also observed to diffuse into the chromia layers.Wagner’s Theory was applied to examine the critical chromium concentration for forming a protective chromia. This prediction indicated alloy concentrations were marginal for chromia formation at both temperatures for the test alloys. The observation of protective chromia formation can be attributed to the effect of other alloying elements, e.g. Al, Mn, Ti, Si etc. Because of the temperature effect on diffusion, the predicted result from Wagner’s Theory showed that the critical chromium concentration needed to form and maintain a protective chromia layer decreased with increasing the oxidation temperature, which is consistent with the experimental observation.The Al and Si oxides formed an additional protective barrier between the matrix and the chromia layer, preventing the diffusion of iron and nickel outwards and therefore increasing the oxidation resistance. Manganese effectively prevented carburization by combining with chromium oxide to form the outermost spinel oxide layer, increasing oxidation/carburisation resistance. Titanium diffused through the chromia layer, accelerating chromium diffusion and leading to higher kinetic rates. Tungsten reduced oxidation resistance by increasing the metal vacancies and therefore outward diffusion of Ni, Fe and Mn through the chromia scale.In general, no significant carbide formation was found in any of the Ni-base alloys in these reaction conditions. At 750℃, carburization due to CO2 reaction was found for 230 alloy but not for 617 and 601 alloys after 500h reaction. However, at 850°C, internal carbides from the reaction were observed for all three alloys. The variation in carburization extent among the different alloys can be attributed to the formation of oxides of aluminum, manganese and silicon, which can impede the inward diffusion of carbon, resulting in the reduction of carburizing kinetics.

Effect of Structural Relaxation on the Indentation Size Effect and Deformation Behavior of Cu–Zr–Based Nanoglasses

In this work, the deformation behavior of as-prepared (AP) and structurally relaxed (SR) Cu–Zr–based nanoglasses (NGs) are investigated using nano- and micro-indentation. The NGs are subjected to structural relaxation by annealing them close to the glass transition temperature without altering their amorphous nature. The indentation load, p, vs. displacement, h, curves of SR samples are characterized by discrete displacement bursts, while the AP samples do not show any of them, suggesting that annealing has caused a local change in the amorphous structure. In both the samples, hardness (at nano- and micro-indentation) decreases with increasing p, demonstrating the indentation size effect. The micro-indentation imprints of SR NGs show evidence of shear bands at the periphery, indicating a heterogeneous plastic flow, while AP NG does not display any shear bands. Interestingly, the shear band density decreases with p, highlighting the fact that plastic strain is accommodated entirely by the shear bands in the subsurface deformation zone. The results are explained by the differences in the amorphous structure of the two NGs.

Integration of finishing and surface treatment of Inconel 718 alloy using high-speed ultrasonic vibration cutting

The successful implementation of high-speed ultrasonic vibration cutting (HUVC) to improve the machinability of the Inconel 718 alloy has been reported in literature. However, the influence of HUVC on the surface integrity of the Inconel 718 alloy has not been investigated. In this context, this study is the first attempt to integrate cutting operations and mechanical surface treatment into one step via HUVC. To this end, an experiment was performed to compare the surface integrity of conventional cutting (CC) and HUVC using coated carbide tools at high cutting speeds (80–240 m/min). The experiment revealed that HUVC led to a lower surface roughness, regular surface micro-texture, deeper subsurface deformation zone (up to 104.47 μm), higher surface micro-hardness rate (by up to ~50%), and higher surface compressive residual stress (−1772 to −2323 MPa) compared to CC. In some occasions, a single HUVC step can be used to satisfy requirements originally addressed over two distinct steps (cutting operation and mechanical surface treatment) by improving surface integrity.

On the differences in shear band characteristics between a binary Pd-Si metallic and nanoglass

Shear band morphology of a binary Pd80Si20 nanoglass (NG) and metallic glass (MG) was investigated using bonded interface indentation technique. The results clearly indicate that the plastic strain in the subsurface deformation zone in NG is accommodated by very fine secondary shear bands in addition to a fewer primary shear bands while in MG it is mainly by primary shear bands. Furthermore, at any given indentation load, the size of the normalized subsurface deformation zone, χ, is found to be higher for NG compared to MG suggesting that the deformation of Pd80Si20 NG is more pressure sensitive and softer than MG. These differences in deformation characteristics between the NG and MG closely related to the intrinsic differences in the glass structure.

Crustal structure of the metasedimentary Kisseynew domain and bounding volcanic–plutonic domains, Trans-Hudson orogen, Canada

The Kisseynew domain (KD) is the largest component of the Paleoproterozoic Trans-Hudson orogen (THO) in Saskatchewan and Manitoba. It is bounded to the north by the Lynn Lake – Leaf Rapids (LL-LR) domain and to the south by the Glennie – Flin Flon (G-FF) complex. The THO was the focus of one of the study areas of Lithoprobe, Canada’s national Earth science research project (1984–2005). To further investigate the crustal structure of the KD and its bounding domains, this study reprocesses reflection line S3a across its northern boundary, analyses four 2.5-D gravity profiles, carries out 3-D gravity inversions for two areas, and replicates results from reflection lines 7 and 10 across the southern boundary of the KD. The reprocessed seismic section enhances the continuity of reflections within the crust. The reflectivity is representative of the complex tectonic development of the boundary zone and clearly identifies a subsurface deformation zone consistent with the boundary. The reflection section also shows that a lower plate (at about 30 to 50 km depth), interpreted as remnant lower crust of the G-FF complex, extends 30 km further northward than in the original section. Lines 7 and 10 illustrate the complex nature of the transition from the KD to the G-FF complex. The gravity analyses show that the variability and complexities of the boundary region between the LL-LR domain and KD, and the G-FF complex and KD, as indicated by the geological and Bouguer gravity maps, extend at depth throughout the crust.

Tribological response and microstructural evolution of nanostructured bainitic steel under repeated frictional sliding

Nanostructured bainitic steels have tremendous potential to be used in structural applications e.g. as rail materials. Strength and toughness in nanostructured bainite can be easily tailored by controlling the lath thickness of bainitic ferrite plates (BF) along with the morphology and volume fraction of retained austenite (RA). However, the wear response under repeated sliding depends on the microstructural evolution with the number of passes and thus is difficult to predict without careful experiments. In the current study, we have made nano-bainitic steels with a range of lath thicknesses from a steel of composition Fe-0.89C-1.59Si-1.65Mn-0.37Mo-1Co-0.56Al-0.19Cr (wt%). Austenitization followed by isothermal holding at 250 °C, 300 °C and 350 °C has been used to make specimens with average bainitic lath thicknesses of about 45, 54 and 89 nm respectively. Depth sensing instrumented indenter with a conical tip has been used to make multiple scratches on all the specimens and the damage has been characterized in the form of depth of scratch, scratch thickness and groove volume using a combination of profilometer and scanning electron microscopy. Specimens transformed at lower isothermal temperature show less wear damage evident in the form of thinner scratch profile, shallower scratch depth and hence smaller wear volume. Moreover, the friction coefficient is found to decrease with a reduction in the austempering temperature. However, the dynamic friction coefficient for all the specimens saturates after around 20 passes of sliding. Cross-sectional imaging of the scratches shows loss of blocky RA, refinement and orientation of the RA and BF laths along the shape of the bottom of groove after repeated sliding. Moreover, the sub-surface hardness decreases for all the specimens after sliding fatigue. However, the specimen austempered at 250 °C shows the lowest friction coefficient, the least material removal and smallest sub-surface deformation zone under conditions of repeated frictional sliding.

Microlubrication machining of 1018 steel: the effect of a biodegradable lubricant on the microstructural integrity

AbstractMicrolubrication is a green machining technique that reduces the amount of cutting fluid during the machining process. Its effect on subsurface microstructural integrity is a very important aspect for the functionality of a machined component, but it is often neglected and requires advanced characterisation techniques. The focus of this study is to investigate the influence of microlubrication using a biodegradable vegetable oil‐based cutting fluid to characterise the subsurface microstructural integrity during end milling of AISI 1018 steel. Vickers microhardness was measured along the cross section of the machined component from the surface edge to inside the bulk, while transmission electron microscopy was conducted inside the subsurface deformation zone to quantify the dislocation densities. It was determined that increased dislocation densities near the workpiece edge resulted in increased microhardness with reduced tool wear. Thus, microlubrication machining is a sustainable green machining process that does not significantly compromise the subsurface integrity of the workpiece material. Copyright © 2017 John Wiley & Sons, Ltd.

On the subsurface deformation of two different Fe-based bulk metallic glasses indented by Vickers micro hardness

Bonded interface technique was employed to examine the nature of subsurface deformation during Vickers micro indentation in two iron-base bulk metallic glasses, (Fe0.9Ni0.1)77Mo5P9C7.5B1.5 (BMG-1) and Fe40Co8Cr15Mo13Y2C16B6 (BMG-2). Quantitative information such as the subsurface deformation zone size was recorded for indentation loads ranging from 200 to 5000 gr. The results showed that the BMG-2 specimens had an average hardness value higher than those observed in the BMG-1 specimens. The trends of the hardness vs. indentation load in the BMG-1 specimens were found to be related to the pressure sensitive index, while in the BMG-2 specimens, the cracking events and deformation-induced creation of free volume were responsible for the hardness tendency change. Observations of the deformation zones indicated that they deformed noticeably through two types of semi-circular and radial shear bands and the density of the radial shear bands was much more in the annealed specimens compared to the as-cast specimens. The relaxed and partially crystallized BMG-2 specimens exhibited cracking, ripple-like pattern as well as cracking and fragmentation, respectively. A simplified R = CP0.5 model was used to analyze the shear band zone size in the subsurface and specimens brittleness.

Effect of temperature on the plastic zone size and the shear band density in a bulk metallic glass

► Subsurface deformation zone of a Zr-based BMG was examined at different temperatures. ► Inter-band spacing increases with increase in temperature. ► Shear band mediated plastic zone remains invariant with temperature. ► Contribution of homogeneous deformation to the total deformation increases with temperature. ► The increased contribution of homogeneous deformation is the reason for increase in pressure sensitivity of BMGs. High temperature bonded interface indentation experiments are carried out on a Zr based bulk metallic glass (BMG) to examine the plastic deformation characteristics in subsurface deformation zone under a Vickers indenter. The results show that the shear bands are semi-circular in shape and propagate in radial direction. At all temperatures the inter-band spacing along the indentation axis is found to increase with increasing distance from the indenter tip. The average shear band spacing monotonically increases with temperature whereas the shear band induced plastic deformation zone is invariant with temperature. These observations are able to explain the increase in pressure sensitive plastic flow of BMGs with temperature.

Microstructure and high temperature wear of the aluminum matrix composites fabricated by reaction from Al–ZrO2–B elemental powders

The microstructural evolution and high temperature wear characteristics of aluminum matrix composites fabricated by reaction of Al–ZrO2–B elemental powders were explored. The amount of the Al3Zr phase in the composites decreased with the increase of the B/ZrO2 mole ratio. When the B/ZrO2 mole ratio reached 2, the Al3Zr components almost diminished and the resultant composites consisted of primarily fine α-Al2O3 and ZrB2 particles. At test temperature of 373K and the applied load of 20N, the wear rate of the composites increased and arrived at the maximum value before decreasing with the further increase of sliding velocity. However, when the test temperature was reached to 473K, the wear rate decreased constantly with the increase of sliding velocity. With the increase of B/ZrO2 molar ratio, both the wear rate and the friction coefficient of the composites decreased, while the subsurface deformation zone increases. The findings help us to broaden the application of aluminum matrix composites in areas where high temperature wear is a limiting factor.

ELECTRICAL RESISTIVITY BASED SHALLOW CRUSTAL DEFORMATION ANALYSIS IN AN ACTIVE SEISMIC ZONE

This paper aims to assess the shallow crustal deformation in a highly seismic-prone zone of northeast India. For that purpose, Tripura University campus has been selected which is nearly 8 km away from Agartala city. The field work was conducted by using electrical resistivity meter. Vertical Electrical Sounding or VES method of resistivity survey was adopted for measuring the electrical resistivity and structural analysis of the study area. Total four VES points were recorded namely near the Department of Physics, Department of Geography and Disaster Management, Teachers’ Residential area and Girls’ Hostel. The recorded data was measured and two different electrical profiles were drawn i.e. (a) Physics building to Geography buildings and (b) teachers’ quarters to Girls’ Hostel. From the electrical resistivity profiles, a clear break in resistivity characters has been observed in the western part which is located near the Tripura University Girls’ Hostel. This clearly proves that a deformation occurred in this area below 4 m depth and it can be very dangerous if a high magnitude seismic slip takes place. From this observation, this hostel is detected as the most risk prone building. Apart from that, the teachers’ quarters near the Girls’ hostel have also been detected as equally risk prone. From this point of view it can be recommended that construction of heavy buildings should be restricted in Tripura University campus as the subsurface deformation zone can create faulting during high magnitude earthquake.

Surface Form Memory in NiTi: Energy Density of Constrained Recovery During Indent Replication

Spherical indentation of NiTi shape memory alloys (SMA) to depths greater than about 3% of the indenter radius results in two-way shape-memory training in a deformation zone beneath the indent. If deep spherical or cylindrical indents are subsequently machined away just sufficiently to remove traces of the original indent (in the martensitic condition), a thermally induced and cyclically reversible flat-to-protruded surface topography is enabled. We term the phenomenon surface form memory. The amplitude of cyclic protrusions, or ‘exdents’, is related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Dislocation generation in this zone is thought to underlie the observed two-way shape-memory (TWSME) training effect. In this article, we show that these cyclic exdents can perform appreciable mechanical work when displacing under load against a base-metal substrate (constrained recovery). This “non-Hertzian” indentation, which appears to be able to exert the full energy density of SMA actuation, may have use for assembly of micromachines, bond-release, microforging, microjoining, electrical switching, microconnectors, and variable heat transfer devices, among many other potential applications.

Indentation-induced two-way shape memory surfaces

A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or “exdents.” Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.

Subsurface deformation during Vickers indentation of bulk metallic glasses

Bonded interface technique was employed to examine the nature of subsurface deformation during Vickers indentation in two kinds of bulk metallic glasses (BMGs), $Pd_{42.1}Ni_{39.77}P_{18.13}$, and $Zr_{56.69}Cu_{26.96}Al_{10.95}Ni_{5.4.}$ Quantitative information such as the shear band spacing, pile-up length, subsurface deformation zone size etc. was recorded for indentation loads ranging from 50 to 5000 g. Experimental results show that both the BMGs have an average hardness value of $\sim$550 VHN with slightly higher hardness at low loads. Observations of deformation zones indicate that they deform appreciably through the shear band mechanism. For both bulk indentation, as well as the interface indentation, the normalized size of the deformation zone was found to be independent of the applied load. Two types of shear bands, radial, and semi-circular in nature, have been observed. These results are compared with similar studies made on ductile metals and silicate glasses.