The reasons for the increase in hardness of alloy tableware

The main reasons for the increase in hardness of alloy tableware are as follows:

The formation of intermetallic compounds: Intermetallic compounds are formed among the various metal elements in an alloy. These compounds have a more stable structure and the metallic bonds are less likely to break, thereby increasing the hardness. For instance, steel is formed by dissolving elements such as C, N, Ni, and Cr in iron. These elements form intermetallic compounds in the iron matrix, making the strength and hardness of steel higher than those of any of the metals that constitute the matrix.

Solid solution strengthening: Certain elements in the alloy dissolve in the base metal to form a solid solution. This solid solution exerts a strengthening effect on the base metal, enhancing the overall hardness and strength. Solute atoms can embed in the interstices of the metal lattice or replace some atomic positions, causing lattice distortion. This distortion hinders the movement of dislocations, thereby enhancing the strength and hardness of the material. For instance, in aluminum alloys, adding elements such as copper, magnesium, manganese, zinc, silicon and nickel to form infinite solid solutions or finite solid solutions can achieve high strength, as well as excellent plasticity and good pressure processing performance.

Lattice distortion: Atoms of different sizes in an alloy can cause lattice distortion, which increases the difficulty of atomic diffusion and thereby enhances the hardness of the material. The newly added atoms are different in size and shape from the original metal atoms, breaking the original regular arrangement and making the relative sliding between atomic layers difficult. Macroscopically, this is manifested as an increase in the hardness of the alloy.

Different crystal structures and spatial arrangements: Different phases and crystal structures exist in alloys. To a certain extent, these different crystal structures prevent the slip of dislocations, thereby preventing plastic deformation and enhancing hardness.

Excess phase strengthening: When the content of alloying elements added to an alloy exceeds its ultimate solubility, a part of the second phase that cannot dissolve into the solid solution will appear during quenching heating, which is called the excess phase. In alloys, the excess phases are mostly hard and brittle intermetallic compounds, which play a role in hindering slip and dislocation movement in the alloy, thereby increasing strength and hardness while reducing plasticity and toughness. The more excess phases there are in an alloy, the better its strengthening effect will be. However, when there are more excess phases, the alloy becomes brittle, resulting in a decrease in strength and plasticity.

Grain refinement: Alloying may refine grains, and an increase in grain boundaries can hinder dislocation migration, which is known as "grain boundary strengthening". For instance, when trace amounts of titanium, zirconium, beryllium, strontium and rare earth elements are added to aluminum alloys, they can form refractory compounds. During the crystallization of the alloy, they act as non-spontaneous crystal nuclei, playing a role in refining the grains and enhancing the strength and plasticity of the alloy.