A variable hardness gradient armor alloy is produced with a liquid-state reaction between a metallic molten pool and a gaseous atmosphere having a small fraction of reactive gas. The content of the reactant gas is varied as the armor is fabricated in order to vary the properties of the resultant material across its thickness and typically include, for example, a hardened outer or initial layer for impact resistance, and at least one inner layer having a lower hardness than the outer layer but greater energy absorption.