Tin-based bearing alloys (Babbitts): What property improvement is primarily obtained by adding antimony (Sb) to tin-based alloys?

Introduction / Context:
Tin-based Babbitt alloys are classic bearing materials. Alloying elements such as antimony and copper adjust hardness, load capacity, and high-temperature behavior to match bearing duty and lubrication regimes.

Given Data / Assumptions:

• Tin is the primary matrix metal.
• Antimony content is a few percent to stiffen the matrix.
• Service involves boundary or mixed lubrication where surface integrity is critical.

Concept / Approach:
Antimony in tin-based alloys forms hard intermetallics and strengthens the matrix, raising hardness and hot strength. This improves load-carrying capability and resistance to creep at elevated temperatures, often described as improved rupture strength and hot hardness for bearing operation.

Step-by-Step Solution:
Recognize the role of Sb: solid-solution plus intermetallic strengthening in Sn matrix.Connect property changes to bearing duty: higher hot hardness supports oil film and reduces wiping at temperature.Select the option listing rupture strength and hot hardness as the core improvements.

Verification / Alternative check:
Materials handbooks list Sn–Sb–Cu Babbitts where Sb increases hardness/strength, while Cu refines structure and further strengthens; combined they raise fatigue resistance.

Why Other Options Are Wrong:
Impact/bonding strength only: not the principal documented effect of Sb in Babbitts. Deformation resistance only and wear resistance only are incomplete; improvements arise primarily via increased hot hardness/load capacity.

Common Pitfalls:
Attributing all bearing performance gains to one element; in practice, Sb and Cu act together, and microstructure and casting practice are crucial.

Final Answer:
Rupture strength and hot hardness are improved