Very different materials are named “Glass,” with Young's modulus (E) and Poisson's ratio (ν) extending from 5 to 180 GPa and from 0.1 to 0.4, respectively, in the case of bulk inorganic glasses. Although glasses have in common the lack of long-range order in the atomic organization, they offer a wide range of structural features at the nanoscale and we show in this analysis that beside the essential role of elastic properties for materials selection in mechanical design, the elastic characteristics (E, ν) at the continuum scale allow to get insight into the short- and medium-range orders existing in glasses. In particular, ν, the atomic packing density (Cg) and the glass network dimensionality appear to be strongly correlated. Maximum values for ν and Cg are observed for metallic glasses (ν∼0.4 and Cg>0.7), which are based on cluster-like structural units. Atomic networks consisting primarily of chains and layers units (chalcogenides, low Si-content silicate, and phosphate glasses) correspond to ν>0.25 and Cg>0.56. On the contrary, ν<0.25 is associated with a highly cross-linked network, such as in a-SiO2, with a tri-dimensional organization resulting in a low packing density. Moreover, the temperature dependence of the elastic moduli brings a new light on the structural changes occurring above the glass transition temperature and on the depolymerization rate in the supercooled liquid. The softening rate depends on the level of cooperativity of atomic movements at the source of the deformation process, with an obvious correlation with the “fragility” of the liquid.

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Elastic Properties and Short-to Medium-Range Order in Glasses

Purpose: Purpose of this paper is the applying of new technology in injection moulding technique and investigation of reinforcement of PC as dispersed phase inside PP matrix (Table 1). Second aim of work is enrichment of those composites by nanoclay and analyzing mechanical behaviour of nanocomposites. Design/methodology/approach: According to design of experiments (DOE) specimens were injection moulded in the shape of rectangular bars. Additionally advanced technology of melt manipulation inside mold cavity after injection was used. To achieve this purpose Ferromatik Milacron injection moulding machine, equipped with externally controlled mold was used. Findings: Addition of nanoclay clearly presents highly reinforced system, especially for neat matrix. Evenly dispersed PC particles within PP majority show reinforcement as well. Inducement of shear rate in injection moulding radically improved absorption of energy in nanocomposite. Research limitations/implications: Different variation of material composition, such combination with other polymers and use of different reinforcements (flexible or either rigid) is required to be checked in the further work. Practical implications: Reinforcement obtained thanks to dispersed phase and nanofillers creates composites with improved mechanical properties. Originality/value: Morphology development reflects on mechanical behaviour. Its manipulation may affect and improve mechanical properties. Use of advanced technologies opens wide range of possibilities in processing of polymer based systems. At present there is limited number of research of processing-structure-properties relationships of polymer-polymer composites and nanocomposites.

Silicon nitride ceramics - review of structure, processing and properties

Silicon nitride-based ceramics contain oxynitride glass phases at the grain boundaries which can impair subsequent high temperature properties. Studies of bulk glasses in the Y-Si-Al-O-N system have been carried out and it has been shown that up to 10 atomic % N can be incorporated into these oxynitride glasses. Nitrogen increases the viscosity, hardness and glass transition temperature of the glasses. Heat treatments of Y-Si-Al-O-N glasses have been carried out and the crystalline phases formed are reported. Further improvements are possible if glass-ceramic processes using two-stage heat treatments are introduced. This paper reviews the development of oxynitride glasses, the effects of nitrogen on properties and reports on the glassceramic heat treatments.

Yttrium oxynitride glasses: Properties and potential for crystallisation to glass-ceramics

Investigation of quench sensitivity of high strength Al–Zn–Mg–Cu alloys by time–temperature-properties diagrams

It has been shown that pressureless sintering of SiC to theoretical density is possible with sintering additives from the system AlN–Y2O3. While commonly a combination of oxides is used such as Al2O3–Y2O3 (–SiO2), the oxynitride additives offer the advantage that only a nitrogen atmosphere is required instead of a powder bed for thermochemical stabilisation at the sintering temperature. The thermal decomposition of AlN is suppressed quite effectively when a moderate nitrogen overpressure is applied, resulting in very small mass loss during densification which only depends on the oxygen content of the SiC starting powder. By varying the mass ratio of β-SiC to α-SiC and applying dedicated post-densification heat treatments, a platelet-strengthened microstructure is obtained which shows enhanced fracture toughness. The platelet formation is attributed to a solution / precipitation process with simultaneous phase transformation from β-SiC to α-SiC, followed by anisotropic grain growth of α-SiC. In the present work, recent progress in the mechanical properties of these materials is reported. By means of a simple surface treatment-annealing in air — it is possible to obtain four-point bending strengths in excess of 1 GPa in liquid phase sintered SiC. The strength retention at temperatures around 1200°C is significantly improved.

High-temperature effects in the fracture mechanical behaviour of silicon carbide liquid-phase sintered with AlN–Y2O3 additives

The application of advances in quench factor analysis property prediction to the heat treatment of 7010 aluminium alloy

Determination of the time–temperature property C curve for aluminium alloys usually involves a large number of quenches and isothermal holds to calibrate a set of constants that describes the shape...

Quench factor analysis of aluminium alloys using the Jominy end quench technique

Glasses have been prepared in the Si-Y-Al-O-N system by melting mixtures of silica, alumina, yttria, and silicon nitride. One particular glass containing 17 equiv% N has been investigated to observe the crystallization at temperatures in the range 1,050--1,300 C. The major crystalline phase observed is Y[sub 2]Si[sub 2]O[sub 7], existing as the [alpha] form below 1,200 C and the [beta] form above this temperature. Properties of the glass-ceramic, including thermal expansion coefficient, hardness, electrical resistivity, and creep have been assessed.

Crystallization and properties of a Si-Y-Al-O-N glass ceramic

The oxidation behaviour of oxynitride glasses in M-Si-Al-O-N system (M = Nd, Y) has been studied in air and under various oxygen pressures. The influence of glass composition on the oxidation resistance was studied at 1075 °C by varying Y Al or Si Al ratios and also by substituting Y by Nd and by varying the nitrogen content. The reactivities in air of the YSiAlON system is studied in the temperature range of 1000–1150 °C. The oxidation resistance of YSiAlON glasses is better than for glasses containing Nd. A pressure law is determined for the YSiAlON system based upon data from oxidation at 1050 and 1075 °C at oxygen pressures in the range of 15–100 kPa. The nature and morphology of oxidised samples were characterised by optical microscopy, XRD and SEM. These investigations reveal that the oxidation of the studied oxynitride glasses is governed by a reaction process where the progress of the internal interface is the limiting step.

R. Flynn

Papers

Yttrium oxynitride glasses: Properties and potential for crystallisation to glass-ceramics

The application of advances in quench factor analysis property prediction to the heat treatment of 7010 aluminium alloy

Quench factor analysis of aluminium alloys using the Jominy end quench technique

Crystallization and properties of a Si-Y-Al-O-N glass ceramic

Oxidation behaviour of yttrium and neodymium oxynitride glasses