Secondary phases in the microstructure of cast alloys can greatly increase the complexity of functional film development, particularly when film growth is induced by diffusion. This paper examines the effect of secondary phases on the diffusion behaviors of aluminum, oxygen, and nitrogen, each of which plays an important role in the formation of functional films on cast aluminum and gray cast iron alloys. In general, a fine and evenly distributed phase morphology improves the uniformity of functional films regardless of whether the secondary phase accelerates or delays mass transfer during diffusion.

In the design of a downhole isolation tool for multi-stage fracturing in the oil and gas industry, a setting component, called slip, was used to set the tool in the casing prior to the hydraulic fracturing operation. The material of the slip is made of gray cast iron with surface hardening requirement. This study investigated the performance of slips treated by induction hardening versus flame hardening. The slip treated by induction hardening produced low hardness and insufficient affected layer. On the other hand, flame hardening generated satisfactory results of case hardening layer by 0.762 mm (0.030 in.) thickness with 50 HRC minimum hardness. The Type E graphite in the raw material was transformed to Type A in the flame hardening process, which is favored in the case hardened layer. The effect of different treatment processes on the affected layer and their microstructural response in gray cast iron was discussed in this study. The isolation tool using the slip treated by flame hardening, together with other proven components, showed successful performance of 82.7 MPa (12 ksi) pressure holding at 177 °C (350 °F) for high pressure and high temperature downhole applications.

Gray cast iron is primarily used for its low cost, high damping capacity, and excellent machinability. These properties are attributed to the presence of free graphite and the high fluidity of the molten metal, which allows for the easy casting of complex parts with thin walls. Applying suitable coatings can enhance wear resistance and broaden the material's range of applications. Niobium carbide, known for its high hardness, is a promising candidate for this purpose. In this study, samples of gray cast iron with the composition 3.47% C, 2.39% Si, 0.55% Mn, 0.15% Ni, 0.65% Cu, and the balance Fe were subjected to a niobizing powder thermo-reactive diffusion treatment. The coating mixture consisted of ferro-niobium, NH 4 Cl, and Al 2 O 3 , and the treatment was conducted at 900 °C for 2 hours. The resulting layers exhibited hardness values of 2000 HV, characteristic of niobium carbides. Micro-adhesive and micro-abrasive wear tests showed a significant increase in wear resistance due to this treatment.