Pack cementation process

The aluminizing of Ni-base alloys via the pack-cementation process has been a commercially viable process for many years [32]. The typical coating morphologies for the... 

Sherardizing is a diffusion process in which the steel parts are heated in the presence of zinc dust or powder in inert medium. Aluminium oxide or sand in amount of 20 % is added to the zinc powder as inert filler and 1 to 2 % halide salts are used as activator. The thermochemical treatment can be carried out in retort, rotated drum or as a pack-cementation process at 350 to 500 °C for three to twelve hours. The structure of the obtained layer is the same as the structure on steel surface after hot-dip galvanizing with a thickness about 50 - 400 pm... 

Pack cementation is widely used to confer oxidation resistance on ferrous alloys. Usually relatively expensive aluminum or binary alloys grade reagent is used during the pack process with aluminum as a source. Pack cementation processes include aluminizing, chromizing, and siliconizing. Components are packed in metal powders in sealed heat-resistant retorts and heated inside a furnace to precisely controlled temperature-time profiles. In the aluminizing process, a source... 

For a platinum-aluminide coating, a thin (typically 8-p,m) layer of platinum is first deposited onto the substrate, usually by a plating process. The second step involves aluminizing for several hours using the conventional packed cementation process to form the platinum-aluminide coating. 

Conventional pack cementation processes are unable to effectively coat internal surfaces such as cooling holes. The coating thickness on these internal surfaces is usually less than on the surface due to limited access by the carrier gas. Access can be improved by pulsing the carrier gas, or by use of a vapor phase coating process. 

Mevrel, R., Duret, C., and Pichoir, R., Pack Cementation Processes, Materials Science and Technology, 2 201 (1986). 

Vapour deposition processes present a certain potential with respect to their applicability to power plant components. This chapter concentrates on addressing the development of chemical vapour deposition (CVD) coatings on 9-12% ferritic-martensitic steels. Two processes have been investigated the in-situ CVD pack cementation process and the fluidised bed CVD (FBCVD) process. 

Eor the pack cementation process, the specimens were put into an alumina retort, surrounded by a powder mixture, composed of a source supplier (Al, Cr, Si or B4C) called the masteralloy, an activator (NH4CI) and an inert filler (AI2O3). Afterwards, the retort was placed in a tubular furnace and heated to the coating temperature for a certain time in inert or reducing environment, i.e. Ar or Ar-10%H2. The detailed experimental conditions are summarised in Table 10.2. 

The Cr deposition by a chloride activated pack cementation process requires high temperatures. In order to enable this kind of treatment on P91, the coating process was combined with the heat treatment of the steel. For 9-... 

A two-step Cr-nAl coating was developed by combining the pack cementation process with the heat treatment of P91 steel. The Cr-rich interlayer is expected to act as an interdiffusion barrier between the Al-rich reservoir and the substrate. 

Aluminide diffusion coating is applied by the classical pack cementation process. This technique has been used since the last century [255-258], even though its industrial and technical applications are more recent [259,260]. It... 

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