Low-Temperature Ductility

Nickel is the alloying element used for improving low-temperature ductility. The addition of 1.5% nickel to 0.25% Cr/0.25%Mo steels provides satisfactory application for moderately low temperatures down to about -50°C. 

Heat treatment by quenching and tempering improves the low temperature ductility of steels such as 0.5 Cr, 0.5% Mo, 1% Ni Type V. For lower-temperature application (below -196°C), up to 9% nickel is used as the sole alloying element. 

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Intermetallic alloys (compounds) are becoming of increasing interest as materials which possess significantly enhanced high temperature capabilities compared to many conventional metallic alloys. However, they suffer intrinsic problems associated with low-temperature ductility and fracture toughness. Two types of... 

The use of PC—ABS blends has grown significantly in the early 1990s. These blends exhibit excellent properties, particularly low temperature ductility, reduced notch sensitivity, and ease of melt fabrication. The blend morphology (229), ABS composition, thermal history (215), PC content and molecular weight (300), processing conditions, etc, all affect the mechanical behavior of PC—ABS blends. These blends have been most frequently used in automotive and other engineering applications. 

STYRENE-MALEIC ANHYDRIDE. A thermoplastic copolymer made by the copolymerization of styrene and maleic anhydride. Two types of polymers are available—impact-modified SMA terpolymer alloys (Cadon ) and SMA copolymers, with and without rubber impact modifiers (Dylark ). These products are distinguished by higher heat resistance than the parent styrenic and ABS families. The MA functionality also provides improved adhesion to glass fiber reinforcement systems. Recent developments include lerpolymer alloy systems with high-speed impact performance and low-temperature ductile fail characteristics required by automotive instrument panel usage. 

The hexagonal close-packed (hep) metals exhibit mechanical properties intermediate between those of the fee and bcc metals. For example, zinc suffers a ductile-to-brittle transition, whereas zirconium and pure titanium do not. The latter and its alloys have an hep structure, remain reasonably ductile at low temperatures, and have been used for many applications where weight reduction and reduced heat leakage through the material have been important. However, small impurities of oxygen, nitrogen, hydrogen, and carbon can have a detrimental effect on the low-temperature ductility properties of titanium and its alloys. 

In general, SMA copolymers, impact-modified SMA copolymers, and glass-filled SMA copolymers have good competitiveness and reasonable processibil-ity in applications which require heat properties greater than general-purpose HIPS and ABS. They provide a low-cost solution where low-temperature ductility is not required. The more ductile SMA-ABS blends have had limited success owing to their poorer flow and tendency to crosslink and decompose at higher temperatures. 

Natural and synthetic rubbers have been studied as additives to alter the viscosity, ductility, and flow properties of road building asphalts. Welbom and Babashak (23) added natural rubber and sulfur to asphalt and reported improved blending conditions, improved stability, increased toughness, and low temperature ductility. 

The nano-level dispersion of clay in thermoplastic olefin (TPO) polymer has potentially provided a platform for its use in automotive body panels of Volvo cars. The governing factors are light weight, consistent physical and mechanical properties, improved aesthetic appearance, improved wear resistance, and low temperature ductility. Recyclability of nano-clay incorporated thermoplastic olefin nanocomposites has provided an opportunity for their use in step assists and trim and panel in Hummer cars. 

Low-temperature ductility is rarely observed in ceramics, which are inherently brittle, but some bulk ceramics show plasticity at ambient temperatures. One example of low-temperature plasticity in MgO is considered here. First, consider a single crystal, where i orientation-dependent properties are of interest. Orientation is one of the factors that influence mechanical properties. It was observed (by etch-pit technique) that the flow in MgO occurs on the 110 (110) slip system. However, it was also found [28] that the 110 (110) slip system contributes to deformation above 600 °C. Details on Plastic deformation in MgO single crystals were presented in Sect. 2.2, Figs. 2.33 and 2.38. Consequently, some information on deformation in polycrystalline ceramics may be of interest. 

Most simply and generally defined, creep is time-dependent deformation under constant stress . Even though creep may occur at relatively moderate temperatures, most ceramics are intended for use at high temperatures, where they are ductile. For ceramics with low-temperature ductility, creep may occur at 0.5 T or even at lower temperatures. The term defined below, indicating homologous... 

RT are considered in terms of their high-temperature performances, specifically under creep conditions. In Sect. 5.2.2, MgO was singled out as an example of a low-temperature ductile ceramic (see Figs. 5.3 and 5.4). Of further interest is RT ductile SrTiOa, which is one of many studied ceramics, due to its interesting and unique features (Fig. 6.24). 

The optimum level of hiphenol in the composition for improved low-temperature impact appears to fall in the range of 26 to 34 mol % (Fig. 14.16). The improved ductility of these copolymers appears to be related to a combination of the presence of biphenol-carbonate-rich microdomains (10 to 20 im) and the low rotational-energy barrier aroimd the biphenyl units in the polymer chain [175]. In addition to low-temperature ductility, the resins maintain a higher percentage of their notched Izod impact strength after heat-aging compared to standard BPA polycarbonate [176-182],... 

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