ISO 14920 pdf download.Thermal spraying — Spraying and fusing of self-fluxing alloys
1 Scope
This standard covers thermal spraying of self fluxing alloys that are simultaneously or subsequently fused to create a homogeneous, diffusion bonded coating.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies.
3 Design considerations
To ascertain whether sprayed and fused alloy coatings are suitable for the intended engineering application, consideration shall be given to the factors in the following sub-clauses. 3.1 Substrate (base metal) 3.1.1 As the process requires the application of heat to fuse the coating to the substrate, consideration shall be given to the possible effects of such heating on the substrate, including: a) distortion; b) scaling; c) the need to stress relieve; d) an irreversible transformation of the mechanical and/or metallurgical properties. Martensitic steels are susceptible to stress cracking and alloys containing significant amounts of C, Al, Ti, Mg, S, sulfides, P, and Nitrogen can create porosity in the coating and may render the substrate liable to stress cracking. 3.1.2 The preparation of the component for a sprayed and fused coating usually includes a reduction of the design dimensions. Consideration shall be given to the effect of such reduction on the required physical properties and the fact that the resultant sprayed and fused coating may have differing physical properties. 3.1.3 The fatigue strength, shock resistance and other properties of the component may be affected by the application of the coating.
4 Self-fluxing alloy selection
4.1 Choice The choice of coating alloy will determine the properties of the final deposit. e.g. a) hardness; b) resistance to wear and corrosion; c) machinability; d) suitability for the application.4.2 Composition The composition of the coating will determine the properties of the final deposit. Consideration shall be given to the effects of the stresses anticipated in service. Substrate alloys which are subject to a martensitic change require a coating alloy with a high ductility. Consideration should also be given to the need for post heat treatment. Guide to approximate hardness of the fused deposit see annex A. 4.3 Final machining 4.3.1 When selecting a suitable self-fluxing alloy, consideration should be given to the machining properties. 4.3.2 Many of the self-fluxing alloys are not machinable with standard tipped tools and can only be finished by using suitable grinding wheels. Manufacturers advice should be sought on suitable machining tools. 4.3.3 As the process involves heating the component to a high temperature, it is recommended that the coating process be completed before final machining of other areas which may be affected by the heat treatment.
5 Preparation of the component
5.1 Preliminary 5.1.1 All components to be treated shall be free from surface contamination such as oil or grease. Particular attention shall be paid to porous components where oil and grease in the pores may exude during the preheating or coating process. 5.1.2 Any prior surface treatments, for example nitriding, electroplating or protective coatings shall be removed before the preparation of the surface to be coated. 5.1.3 When the surface of the component is machined as part of the surface preparation, the machined surface and the form of the ends and/or edges of the prepared area shall be suitable for the coating process. Where the coating is required to terminate at a point other than the end or edge of the component, the edge of the recess shall be machined to provide angle of 30 to 40 degrees, blending smoothly with the adjoining surface. Where the coating shall finish to a square edge, the relevant edge shall be left longer than the proposed finished overall size and machined to the final dimension when the coating process is completed.