Final answer:
The size of the heat-affected zone can be increased by higher temperatures, longer heat exposure, slower cooling rates which contribute to thermal expansion, and thermal stress due to mismatches in expansion coefficients during manufacturing processes.
Step-by-step explanation:
The heat-affected zone (HAZ) size can be increased by various factors during processes such as welding, where materials are joined by applying heat, causing thermal expansion. First and foremost, if the temperature is elevated, the rate of thermal expansion increases, which causes materials to expand not just in length but also in volume and area. When holes expand in the material because of increased temperature, we're seeing thermal expansion in action that directly affects the size of the HAZ. Another factor is the amount of time the material is subjected to heat; a longer duration can increase the HAZ. The rate of heat transfer is also crucial; slower cooling after heating can result in a larger HAZ because the material remains at an elevated temperature for a longer period, allowing for more significant expansion. Mechanical tunneling related to fusion processes, although more relevant at much higher temperatures (like in stars), also highlights that increased temperature can facilitate processes that affect the size of regions under thermal stress.
Another example related to the HAZ is the manufacturing of metal implants, where thermal stress is a concern. A mismatch of expansion coefficients in coatings can lead to cracks due to different rates of expansion under heat. Hence, control of the heat application process can influence the degree of thermal stress and the resulting size of the HAZ.