Alloys have a higher melting point than their constituent metals. The reason behind this behavior is the presence of a second element in the alloy, which causes changes in the crystal structure of the metal.

Crystal Structure and Melting Point
The crystal structure of a metal determines its physical properties, including its melting point. A metal crystal lattice is a regularly repeating pattern of atoms, and the strength of the bonds between these atoms determines the metal's melting point.

Alloy Formation
Alloys are formed by combining two or more metals, or a metal and a non-metal, in varying proportions. The second element in the alloy can cause changes in the crystal structure of the metal, which can affect its melting point.

Effects of Alloying Elements
Alloying elements can have different effects on the crystal structure of metals, which in turn affects their melting points. Some common effects of alloying elements are:

- Solid solution strengthening: Some alloying elements can dissolve in the metal's crystal lattice, making it stronger and increasing its melting point.
- Grain refinement: The presence of a second element can cause the metal crystals to become smaller and more numerous, which can increase its strength and melting point.
- Interstitial alloying: Some elements can fit into the spaces between the metal atoms, causing the metal lattice to become distorted and making it harder to melt.

Examples of High Melting Point Alloys
Some examples of alloys with high melting points are:

- Steel: Steel is an alloy of iron and carbon, and sometimes other elements like chromium, nickel, and manganese. Steel has a higher melting point than pure iron because of the additional elements that strengthen its crystal lattice.
- Tungsten carbide: Tungsten carbide is an alloy of tungsten and carbon. It has a very high melting point (around 2,870°C) because the carbon atoms fit into the spaces between the tungsten atoms, causing the lattice to become distorted and harder to melt.
- Nickel-based superalloys: These alloys contain nickel, cobalt, and other elements like chromium, tungsten, and molybdenum. They are used in high-temperature applications like jet engines because of their high strength and melting points.

Conclusion
In conclusion, alloys have a higher melting point than their constituent metals because of the effects of the alloying elements on the crystal structure of the metal. Alloying elements can cause solid solution strengthening, grain refinement, and interstitial alloying, all of which can increase the metal's melting point.