Evaluation Of Glass-Forming Ability

The emergence of synthetic bulk metallic glasses (BMGs) as a prominent class of functional and structural materials with a unique combination of properties has been an important part of the materials science scene over the past two decades. To date, a number of BMGs have been successfully developed and commercialized for engineering applications utilizing their exceptional properties. However, one of the biggest stumbling blocks for the use of these noncrystalline alloys is still the low glass-forming ability (GFA) of many systems, which is a long-standing problem that is far from being adequately solved. Understanding the nature of glass formation and GFA is the key to developing new BMGs with improved properties and economic manufacturability for industrial applications.

Appreciable progress has been made in understanding the physical insights of bulk glass formation, such as the crystallization mechanisms, alloying effects, liquid fragility, etc., and the macro- and microdeformation mechanisms of BMGs. In this chapter, the focus is placed on how to effectively quantify and represent relative GFA of different glass-forming systems. Previous work on the known GFA indicators and a comprehensive review of recent developments in this area are summarized. One of the main emphases is the establishment of the γ parameter and the demonstration of its better reliability and applicability over all previous GFA indicators. In particular, underlying mechanisms and physical insights of the effective γ criterion will be analyzed in detail. Future directions in understanding and measuring GFA of metallic alloys will also be surmised. Specifically, this chapter contains the following sections:

1.

Brief introduction of previous well-known GFA parameters

2.

The γ indicator and its reliability

3.

Summary of other recently developed GFA criteria/indicators

4.

Limitations of all the newly developed GFA parameters

5.

Prospective directions