Evaluation of Hardness, Sliding Wear and Strength of a Hypoeutectic White Iron with 25%Cr after Heat Treatments

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

Impact of Gercus Formation Erosion and Rock Sliding on Duhok Dam Reservoir – Northern Iraq

The environmental impact was illustrated by rockslide and erosion on the Duhok Dam and its reservoir. The evaluation of the geotechnical characteristics of the Gercus Formation was conducted. The research plan was divided into three phases, field, laboratory, and office works. The fieldwork included studying all the geological phenomena of the region related to the environmental impact. The laboratory work focused on studying the geotechnical properties of the various rock samples taken from the Gercus Formation. Rocklab program was used to define the geotechnical properties of a rock mass. The results indicated the weak resistance of the Gercus Formation rocks to weathering and erosion processes, as well as their weak resistance to sliding. These results indicate a kind of risk for this formation on the stability of the dam, as well as its effect on the size of the reservoir storage, due to erosion and deposition of huge amounts of sediments in the dam reservoir.

Implementation and evaluation of the underwater crack repair in the hollow concrete block of the gravity wharf

Concrete block quay wall is the most popular type of structures in the gravity wharf. The concrete block can be generally categorized into two types: solid and hollow concrete blocks. Compared to the solid concrete block, the hollow concrete block can reduce the usage of concrete significantly and increase the resistance to sliding and overturning. This paper studied the application of hollow concrete blocks in the gravity wharf of Qingdao Port. It was discovered that in the application, the main problem was the crack development in the hollow concrete blocks. The paper first analysed the reason of crack development in the structure by conducting laboratory model tests. It was found that the contact conditions between two hollow concrete blocks was the key of the crack development. In order to improve the performance of the structure of hollow concrete blocks, an effective scheme, which can repair the cracks in the underwater environment and increase the bearing capacity of the gravity wharf, is proposed. The scheme contains two main procedures. The first step is to use the invented mending material to fill up the cracks. The next is to use the grouting technique to bond the rockfill inside the block holes and the hollow concrete blocks together. The model tests, field tests in 1980s and 2010 have proved the effectiveness of the scheme. This paper provides reference for the construction of similar structures.

A Novel Temporary Anchorage Device Aided Sectional Mechanics for Simultaneous Orthodontic Retraction and Intrusion

Closing spaces on light wires with inadequate knowledge and inappropriate mechanics can cause a “roller coaster” effect leading to an improper occlusion. Current knowledge of biomechanics, along with the incorporation of TADs, has made this process less challenging and more predictable. Resistance to sliding is considered the most prominent inhibitor of space closure in archwire-guided space closure or sliding mechanics, in turn delaying treatment duration considerably. In our case, resistance to sliding, primarily binding of the wire in the bracket slot, was nullified with the use of loop and sectional mechanics. This case report is aimed at showcasing the successful treatment of a young lady with a novel clinical setup to retract the canines into the premolar extraction space and simultaneously retract and intrude the anterior segment using sectional archwires and TADs in just under nine months. The current setup with sectional wires and TADs produced an uprighting, and an intrusive effect on the upper incisors during space closure. Additionally, the anchorage design avoided any significant change in the vertical dimension during sagittal correction of the Class II malocclusion. The occlusal plane remained almost stable with good amount of uprighting of the lower incisors following lower space closure too. The use of good biomechanical principles helped us achieve all the treatment goals and objectives in a very short period of time.

Resistance to sliding of orthodontic archwires under increasing applied moments

Background: Orthodontic treatment with fixed appliances involves sliding of brackets along archwires. These movements involve friction, which causes resistance to sliding. In addition, moments cause teeth to tip until binding occurs between the bracket and archwire. The manufacturer of a new TiMolium®Titanium archwire claims material properties superior to β-Titanium, potentially leading to reduced resistance to sliding. Objective: To compare TiMolium archwires with β-Titanium and stainless steel archwires as the current gold standard for sliding mechanics under application of an increasing moment. Materials and methods: A total of 120 stainless steel (Smartclip, 3M, Monrovia, CA) and ceramic self-ligating 0.022″-slot brackets (Clarity SL, 3M) were divided into six equal-sized groups. Resistance to sliding was tested with 0.019″ × 0.025″ TiMolium (TP Orthodontics, La Porte, IN), β-Titanium (3M), and stainless steel (3M) archwires using a custom-designed apparatus to simulate sliding mechanics and application of moments of 1000, 2000, and 3000 g-mm. Results: Using stainless steel brackets, the TiMolium archwires had significantly higher resistance to sliding than stainless steel archwires at all moments tested while there was no difference between TiMolium and β-Titanium. Using ceramic brackets, the resistance to sliding with TiMolium archwires was no different than with stainless steel archwires. Both TiMolium and stainless steel archwires showed significantly lower resistance to sliding than β-Titanium. Conclusion: TiMolium archwires have resistance to sliding intermediary to stainless steel and β-Titanium archwires when clinically relevant moments are applied. Used with the stainless steel brackets, they behave like β-Titanium, whereas used with the ceramic brackets, they behave more like stainless steel.

Process Parameter Impact on Suspension-HVOF-Sprayed Cr2O3 Coatings

Chromium oxide (Cr2O3) is commonly used as an atmospheric plasma-sprayed (APS) coating from powder feedstock in applications requiring resistance to sliding wear and corrosion, as well as amenability to texturing, e.g., in anilox rolls. Recently, high-velocity oxy-fuel spray methods involving suspension feedstock have been considered an extremely promising alternative to produce denser and more homogeneous chromium oxide coatings with lower as-sprayed surface roughness, higher hardness and potentially superior wear performance compared to conventional APS-sprayed coatings. In this study, the impact of process parameters namely auxiliary air cleaning nozzles and a transverse air curtain on suspension high-velocity oxy-fuel-sprayed Cr2O3 suspensions is presented. The produced coatings are characterized for their microstructure, mechanical properties and wear resistance by cavitation erosion. The results reveal the importance of optimized air nozzles and air curtain to achieve a vastly improved coating structure and performance.

Engineering Reactive Clay Systems by Ground Rubber Replacement and Polyacrylamide Treatment

This study investigates the combined performance of ground rubber (GR), the additive, and polyacrylamide (PAM), the binder, as a sustainable solution towards ameliorating the inferior geotechnical attributes of an expansive clay. The first phase of the experimental program examined the effects of PAM concentration on the soil’s mechanical properties—consistency, sediment volume attributes, compactability, unconfined compressive strength (UCS), reactivity and microstructure features. The second phase investigated the effects of GR content, with and without the optimum PAM concentration. An increase in PAM beyond 0.2 g/L, the identified optimum concentration, caused the excess PAM to act as a lubricant rather than a flocculant. This feature facilitated reduced overall resistance to sliding of soil particles relative to each other, thereby adversely influencing the improvement in stress–strain–strength response achieved for ≤0.2 g/L PAM. This transitional mechanism was further verified by the consistency limits and sediment volume properties, both of which exhibited only minor variations beyond 0.2 g/L PAM. The greater the GR content, the higher the mobilized UCS up to 10% GR, beyond which the dominant GR-to-GR interaction (i.e., rubber-clustering) adversely influenced the stress–strain–strength response. Reduction in the soil’s swell–shrink capacity, however, was consistently in favor of higher GR contents. Addition of PAM to the GR-blended samples amended the soil aggregate–GR connection interface, thereby achieving further improvements in the soil’s UCS and volume change behaviors. A maximum GR content of 20%, paired with 0.2 g/L PAM, managed to satisfy a major decrease in the swell–shrink capacity while improving the strength-related features, and thus was deemed as the optimum choice.

Sliding dominates slow-flowing margin regions, Greenland Ice Sheet

On the Greenland Ice Sheet (GrIS), ice flow due to deformation and sliding across the bed delivers ice to lower-elevation marginal regions where it can melt. We measured the two mechanisms of motion using a three-dimensional array of 212 tilt sensors installed within a network of boreholes drilled to the bed in the ablation zone of GrIS. Unexpectedly, sliding completely dominates ice motion all winter, despite a hard bedrock substrate and no concurrent surface meltwater forcing. Modeling constrained by detailed tilt observations made along the basal interface suggests that the high sliding is due to a slippery bed, where sparsely spaced bedrock bumps provide the limited resistance to sliding. The conditions at the site are characterized as typical of ice sheet margins; thus, most ice flow near the margins of GrIS is mainly from sliding, and marginal ice fluxes are near their theoretical maximum for observed surface speeds.

TRIBOLOGICAL PROPERTIES OF Ti-6Al-7Nb ALLOY AFTER ISOTHERMAL OXIDATION

The paper presents the characterization of tribological properties of the Ti-6Al-7Nb alloy before and after isothermal oxidation in different friction couples. Microscopic observations have shown that uniform oxide layers were obtained, which evenly covered the entire surface of the investigated samples. It was found that oxide layers deposited on the Ti-6Al-7Nb alloy substrate contribute to a considerable improvement of the tribological properties. The best resistance to sliding wear was shown by the layer obtained at a temperature of 600°C. It was also shown that presence of oxide layers on the surface of the Ti-6Al-7Nb alloy leads to an increase in the friction coefficient. The highest increase in the value of the friction coefficient was observed for a surface oxidized at 650°C during interaction with an Al2O3 ball. SEM observations of traces of the tribological interaction showed the presence of numerous scratches and fine wear products on the friction surface. For the non-oxidized condition, after interaction with a ball made of bearing steel 100Cr6, the presence was found of alternating, morphologically varied areas which had formed as a result of corrugation wear. Tests have shown that isothermal oxidation eliminates this disadvantageous phenomenon.