This study performs a comprehensive analysis concerning the amount of fine tungsten carbide (WC) grains needed for the appropriate reinforcement of the cobalt (Co) metallic binder in WC-8Co cemented carbides. The goal is to investigate the balance of coarse-to-fine grain distribution to achieve overall improvement of the material’s mechanical and wear properties. All samples possessed the same WC-8Co binder content, therefore, allowing the role of grain size distribution to be tested. It was found that a ratio of 8:1 wt% of coarse to ultrafine grain WC yielded an appropriate balance between material hardness, fracture toughness, and rupture strength. Upon adding grain growth inhibitors vanadium carbide (VC) and chromium carbide (Cr3C2), the overall wear resistance is further improved compared to undoped composites when samples are tested under abrasive wear conditions.

In the sport of curling, stones are slid across an ice sheet, aimed towards a target area. A sliding stone does not move in a straight line, but follows a curled trajectory, deviating in a direction determined by its rotation. As yet, no satisfactory explanation for this motion has been presented, although many attempts have been made. In many of them, the curling motion has been attributed to an asymmetrical distribution of the friction force acting on the sliding stone, typically such that the friction on the rear of the stone (as seen in the direction of motion) is higher than that on the front. In this paper, the motion of a rotating curling stone sliding over ice is calculated, for different assumed distributions of the coefficient of friction in the contact between stone and ice, using a numerical method. It is shown that no redistribution of the friction, no matter how extreme, can explain the observed motion of a real curling stone.

This study performs the comprehensive analysis with regards to the amount of ultrafine WC grains needed for the appropriate reinforcement of the metallic binder in WC-8Co cemented carbides. The rat ...

This work reports on hard part turning of carburizing steels using a PCBN cutting tool in fine machining. Emphasis is on the link between composition of the inclusions in work material and wear mechanisms of the cutting tool. A Ca-treated machinability improved 20NiCrMo steel was included together with three other carburizing steels with different inclusion characteristics.Machining tests were conducted to examine cutting tool life and its balance between excessive flank wear and crater wear. The wear mechanisms were examined using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector.The longest tool life was obtained when cutting the Ca-treated steel. The improved machinability is linked to the deposition of complex (Mn,Ca)S and (Ca,Al)(O,S) protective slag layers that form on the rake face of the cutting tool during machining. Cutting in this steel also resulted in a typical ridge formation in the tool edge crater. Transfer of workpiece material to the rake face crater is characteristic in hard part turning of steel with high cleanliness. This is suggested to be related to the lack of the sulfides that lubricate conventional machinability treated steels, and that the crater wear of low-sulfur steel is more pronounced than for steels with higher sulfur content. (C) 2015 The Authors. Published by Elsevier B.V.

Many products used every day have at least some parts manufactured by sheet metal forming.Sheet metal forming is well suited for mass production and many machines perform aforming step in a matter ...

Thermal fatigue is an important life-limiting factor in die casting moulds. It is observed as a network of fine cracks on the surface exposed to thermal cycling. The crack network degrades the surface quality of the tool and, consequently, the surface of the casting. Surface engineered materials are today successfully utilised to improve the erosion and corrosion resistance. However, their resistance when exposed to thermal cycling is not fully understood. In this work, surface treatments (boriding and Toyota diffusion to give CrC) and physically vapour deposited (PVD) coatings of CrN, as single-layered or duplex-treated (nitriding followed by PVD coating), on hot work tool steel specimens were compared with the untreated reference material by experimental simulation of thermal fatigue. The test is based on induction heating and surface strain measurements by a non-contact laser speckle technique, which enables studies of the surface strain during thermal cycling. Thermal fatigue cracking of a surface engineered tool steel is influenced by the modification of the mechanical properties of the substrate which occurs during the engineering process. With the exception of duplex-treatment, all variants of surface engineering show a tendency to decrease the resistance to thermal fatigue cracking as compared to the reference steel. However, the fact that the duplex-treated PVD CrN coating increased the resistance to thermal fatigue cracking as well as reduces the density of cracks as compared to the single-layered CrN coating, the potential to improve the life and performance in for example die casting applications still prevails.

Curling is an Olympic winter sport in which two teams slide stones across a sheet of ice towards a target area, some 28m away from the release line. The sport has its name from the fact that the trajectory of a rotating stone becomes slightly curled, a fact used to reach open spots or take out opponent stones behind hindering “guarding” stones, etc. By slowly turning the stone clockwise when it is released, it will curl to the right, and vice versa. The resulting sideward deviation is typically slightly more than a metre. This intriguing tribological phenomenon has so far lacked a satisfactory explanation, although many attempts have been presented. In many of them, the curling motion has been attributed to an asymmetrical distribution of the friction force acting on the sliding stone, such that the friction on the rear of the stone (as seen in the direction of motion) is higher than that on the front. In a recent paper, we could show that no such redistribution of the friction, no matter how extreme, can explain the magnitude of the observed motion of a real curling stone. The present work presents an alternative asymmetrical mechanism that actually is strong enough to account for the observed motion. Further, in contrast to previous models, it satisfies other observed phenomena, including the independence of rotational speed of the stone and the strong dependence of the roughness of the stone. The model is backed up by experimental evidence and is based on the specific tribological conditions presented by the contact between a scratched curling stone and a pebbled ice sheet.

Maintaining a reasonably low cutting tool wear when producing forming tools is a general challenge in the development of new forming tool materials. The tool life of a hot forming tool steel (H13) has been significantly improved by reducing its Si-content from 1.0 to 0.06 wt.%. However, this modified H13 (MH13) also displays a reduced cutting tool life due to higher cutting forces and a stronger tendency to form built up layers (BUE) on the cutting edge. This paper explains why. Gleeble tests of MH13 revealed a significantly higher flow stress in the 820–900 °C temperature interval in MH13 compared to H13. Thermo-Calc simulations showed that when reducing the Si-content from 1.0 to 0.06 wt.% the initial temperature for ferrite-to-austenite transformation (A1) was reduced from 900 °C to 820 °C. Knowing that austenite has totally different mechanical and thermal properties than ferrite, the difference in A1 between the two steels explains the higher cutting forces and higher tendency for BUE-formation. The conclusion is that the difference in machinability between H13 and MH13 is primarily related to their difference in A1. An attempt was also made to find a new tool material composition that can combine the wear resistance of MH13 and the good machinability of H13. Thermo-Calc simulations were performed with slightly modified alloying content without changing its properties as a good forming tool material, with the aim to increase A1. For instance, reducing the Mn content from 0.5 to 0.05 wt.% proved to increase A1 from 820 to 850 °C.

A method for determining residual stresses through nanoindentation has been used in order to evaluate the local residual stress in a PVD Ti0.5Al0.5N coating. The influence of residual stress on the ...

This study presents a comparative analysis of surface characteristics and properties of anodised aluminium cylinders produced by sand casting, permanent mould casting, extrusion, and high pressure die casting. Differences in micro structure and distribution of silicon particles in the aluminium, due to the fabrication method and the silicon content in the alloy, resulted in varying thickness of the oxide layers (mean thicknesses between 7 and 19μm) and surface topography. The oxide layer was unevenly thick for the permanent mould cast and the sand cast cylinders, resulting in a surface with higher plateaus and lower areas. This was more prominent for the sand cast surface. The oxide of the extruded cylinder was thick and even and its surface was smooth. The high pressure die cast surface had an oxide that was very thin and uneven. The surfaces displayed different results in the scratch test due to the variations in the surface structure. For the permanent mould cast and the sand cast surfaces the silicon particles present in the oxide deflected the cracks that were formed during the scratching. This resulted in smaller wear debris. The nanohardness values of the oxides had a large scattering due to the inhomogeneous nature of the oxide layers, with pores and particles. However, the highest nanohardness values were between 5000 and 6000MPa for the four surfaces, which is significantly lower than that of sintered alumina. In the micro abrasion test the wear mechanism for all four surfaces was microcutting resulting in chippings.

The “biological pump” is the process by which photosynthetically-produced organic matter in the ocean descends from the surface layer to depth by a combination of sinking particles, advection or vertical mixing of dissolved organic matter, and transport by animals. Particulate organic matter that is exported downward from the euphotic zone is composed of combinations of fecal pellets from zooplankton and fish, organic aggregates known as “marine snow” and phytodetritus from sinking phytoplankton. Previous reviews by Turner and Ferrante (1979) and Turner (2002) focused on publications that appeared through late 2001. Since that time, studies of the biological pump have continued, and there have been >300 papers on vertical export flux using sediment traps, large-volume filtration systems and other techniques from throughout the global ocean. This review will focus primarily on recent studies that have appeared since 2001. Major topics covered in this review are (1) an overview of the biological pump, and its efficiency and variability, and the role of dissolved organic carbon in the biological pump; (2) zooplankton fecal pellets, including the contribution of zooplankton fecal pellets to export flux, epipelagic retention of zooplankton fecal pellets due to zooplankton activities, zooplankton vertical migration and fecal pellet repackaging, microbial ecology of fecal pellets, sinking velocities of fecal pellets and aggregates, ballasting of sinking particles by mineral contents, phytoplankton cysts, intact cells and harmful algae toxins in fecal pellets, importance of fecal pellets from various types of zooplankton, and the role of zooplankton fecal pellets in picoplankton export; (3) marine snow, including the origins, abundance, and distributions of marine snow, particles and organisms associated with marine snow, consumption and fragmentation of marine snow by animals, pathogens associated with marine snow; (4) phytodetritus, including pulsed export of phytodetritus, phytodetritus from Phaeocystis spp., picoplankton in phytodetritus, the summer export pulse (SEP) of phytodetritus in the subtropical North Pacific, benthic community responses to phytodetritus; (5) other components of the biological pump, including fish fecal pellets and fish-mediated export, sinking carcasses of animals and macrophytes, feces from marine mammals, transparent exopolymer particles (TEP); (6) the biological pump and climate, including origins of the biological pump, the biological pump and glacial/interglacial cycles, the biological pump and contemporary climate variations, and the biological pump and anthropogenic climate change. The review concludes with potential future modifications in the biological pump due to climate change.

The surface properties of Fe-rich ferromagnetic Fe-Cr alloys are investigated using a first-principles quantum-mechanical method. In dilute alloys, the surfaces are dominated by Fe, whereas the Cr-containing surfaces become favorable when the bulk Cr concentration exceeds the limit of ∼ 10 atomic per cent. The abrupt change in the surface behavior is the consequence of complex competing magneto-chemical interactions between the alloying atoms. Considering the quantities of various features: equilibrium surface profiles, chemical potentials, segregation energies, surface energies, magnetic moments, mixing energies and pair interactions, within a wider range of bulk and surface concentrations enables us to build a comprehensive picture of the physics of Fe-Cr surfaces. Using the present achievements many previously controversial results can now be merged into a consistent model of Fe-rich Fe-Cr alloys.

Curling is an Olympic winter sport in which 8 players forming two teams slide stones across a sheet of ice towards a target area. The two teams have eight stones each and take turns to slide the stones over to the target area, some 28 m away from the release line. After being released, the stone is only affected by the sliding friction. However, this friction may be somewhat modified by sweeping the ice just in front of the sliding stone, using special curling brooms. Further, the trajectory of the stone becomes slightly curled. By slowly turning the stone clockwise when it is released, it will turn to the right, and vice versa. The best team in each round of 16 stones score one point for each stone resting closer to the target than the best stone from the opponent team.The game makes up a very interesting tribological system, presenting a number of challenging problems. These problems include understanding exactly:what determines the level of friction, and how it is affected by the sweeping,how the roughness of the stone influences the friction, and how the sliding surface should best be prepared to give a stable and repeatable friction,how the intentionally bumpy ice structure influences the friction,the size and distribution of the contact spots between the rough stone and the pebbled ice,the mechanism causing the curl of the stone - Why does the stone curl?.This poster is based on an experimental project, and presents this very intriguing tribological system. It offers some ready explanations and challenges the visiting tribologists to contribute their insights.