Eutectic system

Introduction to Materials Science and Engineering

4 Mar 201816:45

Summary

TLDRThe script discusses the phase diagram of lead-tin solder alloy, traditionally used for soldering due to its low melting point. It explains the concept of solid solution strengthening in alloys, highlighting the melting points of lead (327°C) and tin (232°C). The lead-tin phase diagram reveals a unique eutectic point at 183°C, where a 62% tin alloy melts at a remarkably low temperature. The eutectic alloy solidifies at a single temperature, introducing new boundaries like the eutectic horizontal, solidus, and solvus in the phase diagram.

Takeaways

🔍 The script discusses the lead-tin solder alloy, traditionally common but now being phased out due to lead toxicity concerns.
🔨 Soldering requires a low melting point alloy for ease of melting, and the lead-tin alloy is an example of such a material.
💪 Alloys generally have better strength than pure elements, a concept known as solid solution strengthening.
🌡️ Lead has a melting point of 327 degrees Celsius, and tin has an even lower melting point of 232 degrees Celsius, making them suitable for alloying to create a low melting point solder.
📉 The addition of tin to lead is expected to lower the melting point of the alloy, which is beneficial for soldering applications.
📊 The lead-tin phase diagram is introduced, showing a non-linear relationship between composition and melting point.
📍 The phase diagram reveals a minimum melting point of 183 degrees Celsius for the lead-tin alloy at 62 weight percent tin.
🔬 The phase diagram includes unique features such as a non-continuous liquidus and two solidus lines, indicating the presence of two distinct solid phases, alpha and beta.
📐 The script explains the terms liquidus, solidus, and solvus, which are boundaries separating different phases in the phase diagram.
🧩 The eutectic point at 62 weight percent tin and 183 degrees Celsius is highlighted as a special composition where the alloy melts at a single, low temperature.
🌟 The eutectic alloy, eutectic composition, and eutectic temperature are defined, with the eutectic horizontal being a key feature in the phase diagram.

Q & A

Why is lead tin solder alloy being phased out in many contexts?
-Lead tin solder alloy is being phased out due to concerns about the toxicity of lead.
What is the replacement for lead tin solder alloy?
-Lead-free solder alloys are commonly used as a replacement.