Super 304H is a new generation of advanced austenitic stainless steels that is increasingly being used in superheater/ reheater (SH/RH) sections of thermal ultra-supercritical steam power plants due to its high creep strength combined with good oxidation resistance and microstructure stability. However, recent studies have shown significant microstructural changes and associated degradation in creep performance during long-term service exposure in this alloy. Microstructure evolution during service and its effect on the long-term creep performance has not been comprehensively assessed. In this work, variations in the microstructure of long-term service exposed Super 304H RH tubes (~99,600 hours at 596°C steam temperature) are documented. The results for the ex-service material are compared to well-documented laboratory studies to provide perspective on improved life management practices for this mainstay advanced stainless steel.

A modified stainless steel coating, named as M-SUS here, was prepared by the air plasma spray process (APS) and the high velocity flame spray process (HVOF) and compared with a conventional stainless steel (JIS: SUS316L). Anodic polarization tests using NaCl, HCl solutions, neutral salt spray test, and exposure test in actual tank for HCl storage were employed for the evaluation of corrosion resistance. Structure of the coatings was investigated by use of optical microscope, scanning electron microscope, electron probe micro-analyzer, and transmission electron microscope. It was found that the coating M-SUS exhibited a remarkably superior corrosion resistance by all tests mentioned above, compared with the conventional ones. Although both of the coatings compose of gamma-austenite (γ-Fe) and delta-ferrite (δ-Fe) phases, the coating M-SUS reveals much less oxide with chromium and more delta-phase enriched with molybdenum. Another exposure test using a mixed acid of 25%HNO3 and 75%HCl yielded that the δ-Fe was not etched out but the γ-Fe vanished, that is, the δ-Fe of M-SUS has a strong anti-corrosion property. It is considered that the superior corrosion resistance of coating M-SUS is attributed to the extensive formation of anti-corrosive δ-Fe and inhibition of chromium depletion resulting from oxide formation.

Cladding is a common method of providing corrosion protection of aluminum alloys, which forms an anodic layer in direct and intimate contact with the alloy sheet during cold roll processing. A structural aluminum alloy is clad in a thin layer of a higher purity alloy that is more galvanically reactive. Common examples include 1230 clad on 2024, and 7072 clad on 6061 and 7075. If this clad layer is damaged or removed the underlying structural alloy is exposed and susceptible to corrosion and/or stress corrosion cracking. Kinetic Metallization is a low temperature deposition technique compliant with MIL-STD-3021 that enables repair or replacement of worn or damaged clad layers. Aluminum or Al-Trans coatings are deposited as a new clad coating, and can be subsequently polished to the same mirror finish as the original clad surfaces. This paper presents the techniques developed for repairing worn or damaged Al clad surfaces using the economical Kinetic Metallization process and the qualification tests performed to date for various feedstock powder formulations (Ref 1).

The Kinetic Metallization (KM) process allows the coating and dimensional restoration of interior diameter (ID) surfaces. It is a low temperature, low pressure, solid-state deposition process that is compliant with the recent MIL-STD-3021 cold spray materials deposition standard. The unique attribute of preheating powder particles to enhance ductility within the Kinetic Metallization process allows for high quality coating deposition onto the inner diameter of small-bore components using very short sonic nozzles. Inovati has developed a KM ID Spray Gun that can deposit a coating normal to the surface of the bore down to interior diameter sizes of 80-mm, with depth-to-diameter ratios exceeding 10-to-1. These ID deposition guns, when used with KM systems, can deposit the full range of coatings including structural aluminum alloys for rebuilding damaged forgings, superalloys for corrosion and/or oxidation protection, and hard-phase carbide coatings for wear resistance. This paper presents a case study for rebuilding of damaged 7075-Al forged landing gear outer cylinders requiring ID coating repairs of 0.020-0.030 inches in thickness. A separate study focuses on tungsten-carbide cobalt (WC-17Co) on steel liners and actuating cylinders for replacing hard chrome coatings and repairing worn cylinder bores.

The low temperature Kinetic Metallization (KM) deposition process is compliant with the recently revised MIL-STD-3021 standard for cold spray materials deposition. KM deposition process and equipment was supported through the US Military via multiple Small Business Innovative Research (SBIR) grants leading to delivery of KM deposition equipment to multiple branches. Coating application areas discussed in this paper include wear resistant tungsten-carbide and chromium-carbide hard-phase coatings. These are used for aircraft engines and landing gear surfaces with firm low temperature deposition requirements. Other areas include aluminum and magnesium dimensional restorations, in particular for Aircraft Mounted Accessory Drive (AMAD) gearboxes for F-18 platforms, and land vehicle housings and casings for the US Marines Corps.

Ceramic tiles are widely used as ballistic armor due to their ability to absorb high specific impact energy. However, ceramic materials often exhibit very low ductility and have a tendency to exhibit multiple fractures in spider-web patterns around the point of impact. One method used to introduce ductility is to encapsulate the tile in a metal jacket, or to provide a strongly adhered metallic backing plate. Aluminum and titanium metals are of primary interest to decrease the overall weight of the armor material system. The low temperature Kinetic Metallization (KM) process allows direct deposition of the metals onto the ceramic tiles. This is not possible with thermal spray processes due to the extreme mismatch in thermal expansion and adverse metallic-ceramic chemical reactions at high temperatures. Kinetic Metallization has been used to deposit aluminum and titanium coatings onto silicon carbide (SiC) and proprietary ceramic matrix composite (CMC) tiles. Ballistic testing of coated tiles has shown decreased fracturing of the armor material, leading to improved performance for subsequent impacts.

The repair of damaged Ion Vapor Deposition Aluminum coatings on high strength steel aircraft components has generally required the use of brush plating with hazardous materials including cadmium. Inovati has developed a unique Al-Trans (aluminum-transition metal) coating using the Kinetic Metallization process that permits repairs of IVD-Al coatings on high strength steels. Originally the Al-Trans coating formulation was developed for commercial application on telecommunication equipment steel racks as an electrically conductive grounding strip with excellent corrosion resistance. Recent research was completed with NAVAIR to further develop this coating formulation and the Kinetic Metallization process for repair of IVD-Al coatings on aircraft components. This presentation will describe the KM repair process and the tests completed to qualify the repaired coatings. Inovati has recently developed a KM-Mobile Coating System with a handheld Spray Gun for the field repair of corrosion damaged magnesium and aluminum alloy aircraft components.