Hardness and Wear Resistance: One of the most important properties for many applications is hardness. As deposited, the micro-hardness of EN coatings is about 500 to 700 HK100 . That is approximately equal to 45 to 58 HRC and equivalent to many hardened alloy steels. Heat treatment causes these alloys to precipitation harden and can produce hardness values as high as 1100 HK100. That is equal to most commercial hard chromium coatings. For some applications, high temperature treatments cannot be tolerated because of part distortion or because of their effect on the substrate. For these, it is sometimes possible to use longer times and lower temperatures to obtain the desired hardness. Treatment at 375ºC (700ºF) for 1 to 2 hours, and at 290ºC (550ºF) for 10 to 12 hours are commonly used for EN deposits. Those treatments can produce hardness values of 950 to 1000 HK100. Treatments at 260ºC (500ºF) are also occasionally used, although the resulting hardness is lower. At temperatures of 230ºC (450ºF) and below, only a minimal increase in hardness is obtained. Accordingly such treatments are only rarely used, except for hydrogen de-embrittlement or adhesion improvement. EN coatings also have excellent hot hardness. Up to about 400ºC (750ºF) the hardness of heat treated EN is equal to or better than that of hard chromium coatings. Internal Stress: The total stress in an EN deposit is composed of thermal and intrinsic stresses. Thermal stress results from deposition that occurs at elevated temperatures when the coefficient of thermal expansion is different for the substrate and the plated coating. As the plated piece cools, different shrink rates develop either a tensile or compressive force in the plated layer. Tensile intrinsic stress is caused by distortions in the crystal lattice that result from extraneous ions or hydrogen in the film. In every case where hydrogen is present, the deposit from an electroless solution will shrink when it is heated. Sudden shrinkage typically causes cracking of the coating. Slow annealing may actually cause diffusion of the plate into the substrate. For this reason many plating specifications require a period of annealing shortly after the parts are plated. Electroless solutions are dynamic in composition and are constantly changing from the build up of reaction by-products that can influence the intrinsic stress. When the total stress in the coating is greater than the adhesive strength to the substrate, the layer can blister and peel. If the total tensile stress exceeds the tensile strength of the coating, the deposit will spontaneously crack. Generally it is accepted that low compressive stress is ideal since it improves the fatigue life of the substrate and is somewhat beneficial to adhesion. High tensile stress on the other hand, will yield reduced fatigue life and poor corrosion resistance. Traditional High & Mid Phos solutions would normally start slightly tensile or compressive, and the stress would rise as the solutions aged. The exact figures would depend on the phosphorus concentration in the deposit. Low phosphorus solutions normally remain slightly tensile throughout the bath life. Higher tensile stress is one of the main limitations on achieving good electroless nickel deposits from older plating solutions. NiKlad ELV deposits stress tends to be slightly more tensile with new solutions but without the typical stress climb seen in older traditional baths. This means that they can give good adherent deposits for longer, and is especially true for the medium and high phosphorus baths. 9