Interaction between the coating characteristics of galvanneal steel and forming parameters during flat die drawing

Galvanneal steel is considered to be better for automotive applications than its counterpart, galvanized steel, mainly because of its superior coating and surface properties. Galvanneal steel is produced by hot dipping sheet steel in a bath of molten zinc with small, controlled, levels of aluminium, followed by annealing which creates a Fe-Zn intermetallic layer. This intermetallic layer of the coating improves spot weldability and improves subsequent paint appearance. However, if the microstructure of the coating is not properly controlled and forming parameters are not properly selected, wear of the coating could occur during stamping. Frictional sliding of the sheet between the tool surfaces results in considerable amount of coating loss. An Interstitial Free steel with a Galvanneal coating of nominally 60g/m2 was used for the laboratory experiments. Flat Face Friction (FFF) tests were performed with different forming conditions and lubricants to simulate the frictional sliding in stamping. Glow-Discharge Optical Emission Spectrometry (DG-OES) was used to measure the change in the coating thickness during sliding. Optical microscopy was considered for imaging the surfaces as well as an optical method to compare the changes in the coating thickness during the forming. The change to the Galvanneal coating thickness was found to be a function of forming parameters.

Pin on disc wear investigation of nitrocarburised H13 tool steel

Nitrocarburised H13 disks were tested in dry, sliding wear against a stationary ruby ball (pin). Three different 4 h nitrocarburising treatments were compared, using N2/NH3/CO2, N2/NH3/natural gas and N2/NH3 gas mixtures, resulting in compound layers of varying thickness, hardness, porosity and oxide morphology. During mild, oxidative wear, with the formation of abrasive wear debris, the most brittle and oxidised surfaces performed poorly. Polishing to a bright, reflective finish greatly reduced wear. However, the N2/NH3/CO2 sample also frequently maintained a 'very mild' wear regime, owing to the formation of a protective film between the wear surfaces, and resulting in a lowering of the friction coefficient. This treated surface was porous and covered in a complex layer of coarse oxide+epsi-carbonitride. Nitrocarburised samples and wear tracks were characterised by optical microscopy, SEM, atomic force microscopy and stylus profilometry.

Ferritic nitrocarburising of tool steels

Four different tool steel materials, P20, H13, M2 and D2, were nitrocarburised at 570°C in a fluidised bed furnace. The reactive diffusion of nitrogen and carbon into the various substrate microstructures is compared and related to the different alloy carbide distributions. The effect of carbon bearing gas (carbon dioxide, natural gas) on carbon absorption is reported, as well as its influence on compound layer growth and porosity. Partial reduction of Fe3O4 at the surface resulted in the formation of a complex, epsi-nitride containing oxide layer. In H13, carbon was deeply absorbed throughout the entire diffusion zone, affecting the growth of grain boundary cementite, nitrogen diffusivity and the sharpness of the compound layer: diffusion zone interface. When natural gas was used, carbon became highly concentrated in the compound layer, while surface decarburisation occurred with carbon dioxide. These microstructural effects are discussed in relation to hardness profiles, and compound layer hardness and ductility. The surfaces were characterised using glow discharge optical emission spectroscopy, optical and scanning electron microscopy and X-ray diffraction.

Microstructure evolution of TI-SN-NB alloy prepared by mechanical alloying

In the present study, Ti-16Sn-4Nb alloy was prepared by mechanical alloying (MA). Optical microscopy, scanning electron microscopy combined with energy dispersive X-ray analysis (SEM-EDX), and X-ray diffraction analysis (XRD) were used to characterise the phase transformation and the microstructure evolution. Results indicated that ball milling to 8 h led to the formation of a supersaturated hcp α-Ti and partial amorphous phase due to the solid solution of Sn and Nb into Ti lattice. The microstructure of the bulk sintered Ti-16Sn-4Nb alloy samples made from the powders at shorter ball milling times, i.e. 20 min- 2 h, exhibited a primary α surrounded by a Widmanstätten structure (transformed β); while in the samples made from the powders at longer ball milling times, i.e. 5- 10 h, the alloy evolved to a microstructure with a disordered and fine β phase dispersed homogeneously within the α matrix. These results contribute to the understanding of the microstructure evolution in alloys of this type prepared by powder metallurgy.

Exploring the contribution of different types of cited materials to marketing knowledge over time : a citation analysis

This paper examines the degree to which articles appearing in JM, JMR, and JCR cite different types of references (journals, books, book chapters, conference proceedings, professional and popular press, and “others”) between 1975 and 2003. The results suggest that the number of citations to journals articles has increased over time and there have been significant falls in reference to non-journal sources of materials. References to some non-journal sources (i.e., newspaper and professional materials) have increased in JCR and JMR, but decreased in JM. The impact of shifts in the types of citation materials on knowledge development is also discussed.

Microengineering of supramolecular soft materials by design of the crystalline fiber networks

Crystalline spherulitic fiber networks are commonly observed in polymeric and supramolecular functional materials. The elasticity of materials with this type of network is low if interactions between the individual spherulites are weak (mutually exclusive). Improving the elasticity of these materials is necessary because of their important applications in many fields. In this work, the engineering of the microstructures and rheological properties of this type of material is carried out. A small molecule organogel formed by the gelation of N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol (PG) is used as an example. The elasticity of this material is improved by controlling the thermodynamic driving force, the supersaturation of the gelator, and by using a selected copolymer additive to manipulate the primary nucleation of GP-1. Because of the weak interactions between the GP-1 spherulites, with the same fiber mass, the elasticity of GP-1/PG gel is less than half of those of the other two gels formed by GP-1 and 2-hydroxystearlic acid in solvent benzyl benzoate (BB), which are supported by interconnecting spherulitic fiber networks. This work develops a robust approach to the engineering of supramolecular functional materials especially those with mutually exclusive spherulite fiber networks.

Application of advanced analytical techniques to study structure-property relationship of hot rolled high strength low alloy steel

The microstructure-property relationship in conventional high strength low alloy (HSLA) steel was evaluated using data obtained from transmission electron microscopy (TEM) and atom probe tomography (APT). Atom probe tomography allowed the characterisation of fine TiC particles with average radius of 3±1·2 nm that were not observed by TEM. The increase in the yield strength of steel due to the presence of fine precipitates was calculated to be 128 MPa.

Fabrication and characterisation of microporous titanium

Microporous titanium was fabricated by a special powder metallurgy process and the microstructure and the mechanical properties of the material were characterised by scanning electron microscopy and quasi-static compression. The pore sizes and porosities of the samples are ranged of 10-50 μm and 40-65%, respectively. Macroporous Ti samples with the pore sizes ranged from 500 to 800 μm were also prepared by the similar process for comparison. The microporous Ti exhibits not only a very different deformation behaviour from the macroporous Ti but also lower flow stress than the latter, completely different from those observed in common porous metals.

Understanding in-vivo abrasion fatigue or common suture materials used in arthroscopic and open shoulder surgery

In orthopaedic surgery the reattachment of tendon to bone requires suture materials that have stable and durable properties to allow healing at the tendon-bone interface. Failure rates of this type of surgery can be as high as 25%. While the tissue suture interface is a weak link, proportions of these failures are caused by in-vivo abrasion of the suture with bone and suture anchor materials. Abrasion of the suture material results from the movement of the suture through the eyelet by the surgeon during surgery, or with limb movement after surgery as the suture is not rigidly restrained within the eyelet. During movement the suture is subjected to bending and frictional forces that can lead to fatigue induced failure. This paper investigates the mechanism of bending abrasion fatigue induced failure of number two grade braided sheath only and braided sheath/multifilament core sutures. Sutures were oscillated over a stainless steel wire at low frequency under load in a dry state to simulate the bending and frictional forces between suture and eyelet. Failure mechanism was determined by video microscopy of the suture during abrasion combined with optical microscopy analysis of partially and fully abraded sutures. Braided only structures had high friction loading on the small number of fibres at the abrasion interface. This caused rapid single fibre breakages that accumulate to cause suture failure. The addition of ultra-high molecular weight polyethylene core fibres to a braided suture distributed the applied load across multiple fibres at the abrasion interface. This improved abrasion resistance by 15-20 times that of braided sheath alone.

Fabrication of meso-porous sintered metal thin films by selective etching of silica based sacrificial template

 Meso-porous metal materials have enhanced surface energies offering unique surface properties with potential applications in chemical catalysis, molecular sensing and selective separation. In this paper, commercial 20 nm diameter metal nano-particles, including silver and copper were blended with 7 nm silica nano-particles by shear mixing. The resulted powders were cold-sintered to form dense, hybrid thin films. The sacrificial silica template was then removed by selective etching in 12 wt% hydrofluoric acid solutions for 15 min to reveal a purely metallic meso-porous thin film material. The impact of the initial silica nano-particle diameter (7–20 nm) as well as the sintering pressure (5–20 ton·m−2) and etching conditions on the morphology and properties of the final nano-porous thin films were investigated by porometry, pyknometery, gas and liquid permeation and electron microscopy. Furthermore, the morphology of the pores and particle aggregation during shear mixing were assessed through cross-sectioning by focus ion beam milling. It is demonstrated that meso-pores ranging between 50 and 320 nm in average diameter and porosities up to 47% can be successfully formed for the range of materials tested.

Atom probe tomography at the University of Sydney

Summary: The Australian Microscopy & Microanalysis Research Facility (AMMRF) operates a national atom probe laboratory at The University of Sydney. This paperprovides a brief review and update of the technique of atom probe tomography (APT),together with a summary of recent research applications at Sydney in the scienceand technology of materials. We describe recent instrumentation advances such asthe use of laser pulsing to effect time-controlled field evaporation, the introductionof wide field of view detectors, where the solid angle for observation is increased byup to a factor of ∼20 as well as innovations in specimen preparation. We concludethat these developments have opened APT to a range of new materials that werepreviously either difficult or impossible to study using this technique because of theirpoor conductivity or brittleness.

Synergistic coassembly of two structurally different molecular gelators

Coassembly of molecules can produce materials with improved properties and functionalities. To this end, achieving a molecular level understanding of the interactions governing the coassembly is essential. In this work, two molecular gelators with significantly different structures and main intermolecular forces for assembly were coassembled. The elastic moduli of the hybrid gels are more than 1 order of magnitude higher than those of the gels formed by the individual gelators, showing an obvious synergistic effect. The interactions between the gelators were investigated with confocal microscopy and both one-dimensional and two-dimensional nuclear magnetic resonance. It was found that the two gelators coassemble to form fibers due to the nonspecific van der Waals interactions between their alkyl chains and the specific interactions between their functional groups. Switching from one gelator-dominated fiber network to the other gelator-dominated fiber network was achieved at a critical molar ratio of the gelators. The two gelators serve as additives of each other to tune the nucleation and growth of the fiber networks. The observations of this work are significant to the development of materials with improved properties by coassembly of different molecules.