Thermal tempering of glass

AbstractDue to their very low thermal conductivities and large thermal expansion values, bulk metallic glasses (BMGs) undergo differential cooling during processing. Large thermal gradients are generated across a specimen leading to residual stress buildup. A thin surface layer contains compressive stresses balanced by tension in the middle. Such stresses can not only influence the mechanical behavior of BMGs, but they can also lead to problems during manufacturing of large or intricate components. Analytical and finite element modeling was used to predict the values and distribution of such stresses as a function of processing conditions. Neutron diffraction measurements were then performed on model specimens which included crystalline phases as “strain gages”. It was shown that significant stresses, on the order of several hundred MPa, can be generated in BMGs. Modeling and diffraction results are presented and their implications discussed.

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Simulated Thermal Tempering versus Sudden Temperature Change and Short-Term Survival of Fingerling Rainbow Trout

North American Journal of Aquaculture ◽

10.1577/1548-8454(2003)065<0067:sttvst>2.0.co;2 ◽

2003 ◽

Vol 65 (1) ◽

pp. 67-69 ◽

Cited By ~ 6

Author(s):

Mark A. Smith ◽

Wayne A. Hubert

Keyword(s):

Rainbow Trout ◽

Temperature Change ◽

Short Term ◽

Term Survival ◽

Thermal Tempering ◽

Sudden Temperature Change ◽

Short Term Survival

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Thermal Tempering of Bulk Metallic Glasses

MRS Proceedings ◽

10.1557/proc-754-cc1.9 ◽

2002 ◽

Vol 754 ◽

Author(s):

Cahit C. Aydiner ◽

Ersan Üstündag

Keyword(s):

Metallic Glasses ◽

Casting Process ◽

Glass Forming Ability ◽

Stress Generation ◽

Copper Mold ◽

Glass Forming ◽

Viscoelastic Models ◽

Compressive Stresses ◽

Thermal Tempering ◽

Stress Profiles

ABSTRACTThe recent development of multi-component alloys with exceptional glass forming ability has allowed the processing of large amorphous metal samples. The possibility of formation of thermal tempering stresses during the processing of these bulk metallic glass (BMG) specimens was investigated using the (1) instant freezing, and (2) viscoelastic models. Both models yielded similar results although from vastly different approaches. It was shown that fast convective cooling of Zr41.2Ti13.8Cu12.5Ni10Be22.5 plates could generate significant compressive stresses on the surfaces balanced with mid-plane tension. The crack compliance method was then employed to measure the stress profiles in a BMG plate that was cast in a copper mold. These profiles were roughly parabolic suggesting that thermal tempering was indeed the dominant residual stress generation mechanism. However, the magnitude of the measured stresses (with peak values of only about 1.5% of the yield strength) was significantly lower than the modeling predictions. Possible reasons for this discrepancy are described in relation to the actual casting process and material properties.

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