1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2008 SAE International All rights reserved. No part of this publication may
3、 be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) F
4、ax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgAMS2448AAEROSPACEMATERIALSPECIFICATIONIssued 2004-10 Revised 2008-06 Superseding AMS2448 Application of Tungsten Carbide Coatings on Ultra High Strength Steels High Velocity Oxygen / Fuel Process RATIONALEAMS2448A resul
5、ts from a Five Year Review and update of this specification. 1. SCOPE 1.1 Purpose This specification covers engineering requirements for applying tungsten carbide thermal spray coatings to ultra high strength steels (220 ksi and above) utilizing high velocity oxygen fuel (HVOF) combustion driven pro
6、cesses and the properties for such coatings. The processes and procedures herein apply only to the properties of the as-deposited coating.1.2 Application This process has been used typically to provide coatings that possess lower porosity and higher adhesive and/or cohesive strength than generally a
7、ttainable with plasma spray and for applications requiring wear, heat, and corrosion resistance or dimensional restoration that were traditionally chrome plated. However, usage is not limited to such applications.1.3 Safety - Hazardous Materials While the materials, methods, applications, and proces
8、ses described or referenced in this specification may involve the use of hazardous materials, this specification does not address the hazards which may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and
9、 to take necessary precautionary measures to ensure the health and safety of all personnel involved. 2. APPLICABLE DOCUMENTS The issue of the following documents in effect on the date of the purchase order forms a part of this specification to the extent specified herein. The supplier may work to a
10、subsequent revision of a document unless a specific document issue is specified. When the referenced document has been cancelled and no superseding document has been specified, the last published issue of that document shall apply. Copyright SAE International Provided by IHS under license with SAENo
11、t for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AMS2448A - 2 -2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. AMS6454 S
12、heet Steel, Strip, and Plate, 1.8Ni - 0.80Cr - 0.25Mo (0.38 - 0.43C) (SAE 4340), Consumable Electrode Melted AMS6484 Steel, Bars, Forging, and Tubing, 0.80Cr - 1.8Ni - 0.25Mo (0.38 - 0.43C) (SAE 4340), Normalized and Tempered AMS7881 Tungsten Carbide-Cobalt Powder, Agglomerated and Sintered AMS7882
13、Tungsten Carbide-Cobalt Chrome Powder, Agglomerated and Sintered SAE J442 Test Strip, Holder, and Gage for Shot Peening 2.2 ASTM Publications Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: 610-832-9585, www.astm.org. ASTM C 633 Adhesio
14、n or Cohesive Strength of Flame-Sprayed Coatings ASTM E 384 Microhardness of Materials 3. TECHNICAL REQUIREMENTS 3.1 Equipment 3.1.1 Torch A specially constructed gun that utilizes combustion products to generate a high velocity gas stream for heating of the coating material to a molten or plasticiz
15、ed state, and transfer of the coating material to the work piece shall be used. The torch shall be microprocessor-controlled and fitted with an automated device for regulating the gas(es) and fuel(s). The torch shall be mounted on an automated manipulating device during the deposition process to mai
16、ntain a constant working distance and traverse rate or maintained in a fixed position with the component mounted on a manipulating device that will maintain a constant working distance. 3.1.2 Gauges 3.1.2.1 Pressure gauges shall have a minimum accuracy of 1.5% of full scale. 3.1.2.2 Flow meters shal
17、l have a minimum accuracy of 2% of full scale. 3.1.3 Powder Feeder The powder feed system shall supply a metered flow of material. 3.2 Materials 3.2.1 Gases and fuels specifications used by the processor for procurement shall be acceptable to the cognizant engineering organization. 3.2.2 Coating mat
18、erial shall conform to AMS7881 or AMS7882 unless otherwise specified by the cognizant engineering organization. All powders shall be dry, free flowing and uniformly blended. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted withou
19、t license from IHS-,-,-SAE AMS2448A - 3 -3.3 Preparation 3.3.1 Cleaning Surfaces to be coated shall be thoroughly cleaned to remove oil, grease, dirt, paint and other foreign material. Final cleaning shall take place no more than four hours prior to coating. Cleaning procedures shall not embrittle,
20、pit, or damage surfaces to be coated. 3.3.2 Masking Parts shall be masked by any appropriate means to protect all surfaces that are not being coated. 3.3.3 Surface Conditioning After cleaning, surfaces to be coated shall be grit-blasted with aluminum oxide blast media at 60 to 80 psi (414 to 552 KPa
21、) and 6 to 8 inches (152 to 203 mm) standoff distance to clean and prepare the surface for HVOF deposition. Grit shall be free from moisture, oil, dirt and other contaminants. Grit size shall be of the finest possible size necessary to achieve a 120 to 150 Ra surface roughness, but shall never be co
22、arser than 54 grit. A surface profilometer shall be used to verify the proper surface conditioning for each procedure used. 3.4 Application 3.4.1 Process The parameters for gas flows and pressures, powder feed rates, and spray distance, as well as deposition rates and traverse speeds shall be determ
23、ined by a statistical method designed to achieve the desired coating properties specified by this document and/or the cognizant engineering organization. 3.4.2 Preheating Surfaces to be coated shall be heated to remove moisture, Surface temperature shall not exceed 350 F (177 C). Preheating may be a
24、ccomplished with the torch or by other suitable means and shall be monitored as specified in 3.4.3.4. 3.4.3 Coating The coating material shall be deposited on the designated surface in sufficient thickness to permit finishing to specified dimensions.3.4.3.1 Areas on which coating is optional must be
25、 prepared and handled in the same manner as the area on which coating is required and adhesion requirements still apply. 3.4.3.2 A spray angle of 90 5 should be maintained. For cylindrical components, angle is measured relative to the centerline axis of the cylinder. For any application that require
26、s a spray angle at less than 85, all test specimens shall be sprayed at the same angle as the component and all minimum mechanical property requirements will apply. 3.4.3.3 Spray deposition shall be continuous except for interruptions to measure coating thickness and/or for cooling cycles to maintai
27、n part below maximum allowable temperature. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AMS2448A - 4 -3.4.3.4 Substrate Temperature Unless otherwise specified, maximum temperature of the subs
28、trate during preheating and coating application shall be controlled to not exceed 350 F (177 C). Temperature measurements shall be made utilizing a laser-sighted infrared (IR) thermometer with adjustable emissivity (0.1 to 0.99) and response time of less than 1 second. Measurement location shall be
29、taken on the parent metal adjacent to the edge of the coating as it traverses the area to be coated. If geometric or part size constraints do not allow this procedure to be followed, then the temperature shall be measured immediately adjacent to the coated area along the same path of travel as the g
30、un plume. Emissivity shall be set to a standard value for high strength steel. Resolution of the IR thermometer shall be 1 C or 1 F, depending on the scale used and spot diameter should be less than 2.5 inch (64 mm) or equivalent to the actual diameter of the IR beam. 3.4.4 Test Specimens Specimens
31、required under 3.7 shall be coated, as far as practicable, using the process procedures identified on the Coating Process Control Sheet (see Figure 1) with the parts that they represent. Specimens representing components rotated under the spray shall be sprayed at the same rotational speed and incre
32、mental step rate as the component. If there are multiple application angles on the same component, each of the deposition angles shall be evaluated with specimens for compliance with minimum mechanical property limits. Specimens shall be evaluated prior to coating application on production component
33、s. 3.4.5 Specimen Material Bond strength specimens shall be fabricated from AMS6484, heat treated to produce a hardness 40 HRC minimum and no higher than the hardness of the component substrate. Metallographic and bend test specimens shall be fabricated from AMS6454 and heat treated to produce a har
34、dness of 40 HRC minimum. Alternatively, test specimens can be made from the same material, in the same condition as the component. 3.5 Surface Finishing Procedures for finishing shall be in accordance with the cognizant engineering organizations specifications. 3.6 Properties 3.6.1 Adhesion 3.6.1.1
35、Bend Test Specimens prepared and tested in accordance with 3.7.1 shall not show separation of the coating from the substrate, when examined visually without magnification. Cracking of the coating and minimal separation at the specimen edges shall be considered acceptable. 3.6.1.2 Bond Strength Speci
36、mens, prepared and tested in accordance with 3.7.2, shall be 10 ksi (69 MPa) minimum. 3.6.2 Coating Hardness The coating hardness, tested in accordance with 3.7.3, shall be HV300g950 minimum. 3.6.3 Microstructure A detailed standard procedure for metallographic specimen preparation and examination s
37、hall be used to ensure consistent results as in 4.4.1. Examination of a suitably prepared cross-sectioned specimen shall show the coatings to be free from cracks and delaminations. Repolishing can only be performed on specimens that show flaws induced by the polishing method. Oxide content cannot be
38、 induced and is not grounds for repolishing. Microstructural properties shall be evaluated in accordance with the following: Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AMS2448A - 5 -3.6.3.1
39、Voids and oxides shall be uniformly distributed and not greater than 1% in any field of view (approximately 0.02 inch (0.5 mm) length) when examined at 400X magnification on the cross sectioned specimen. Any single void greater than 0.002 inch (0.05 mm) shall be cause for rejection. 3.6.3.2 Unmelted
40、 Particles None in any field of view (approximately 0.04 inch (1.0 mm) length) when viewed at 200X magnification on the cross sectioned specimen. 3.6.3.3 Interface Contamination of the coating at the substrate interface with surface preparation media shall not exceed 10% in any field of view (approx
41、imately 0.04 inch (1.0 mm) length) when viewed at 200X magnification on the cross-sectioned specimen. Any coating separation at the interface will not be acceptable. Separation is defined as gap between the coating and substrate greater than 0.002 inch (0.05 mm) in length following directly along th
42、e bond line. Any length less than this will be considered acceptable voids or porosity. 3.6.4 Carbide Distribution In any 400X field of view, all carbides shall be uniformly distributed with no banding or clustering. 3.6.5 Residual Stress Coatings shall be evaluated for residual stress by preparing
43、and spraying a standard Almen Type “N” strip in identical fashion as the component being coated. Both the surface to be coated and uncoated surfaces of the Almen strip shall be grit-blasted to minimize curvature of the Almen strip to less than 0.002 inches (0.05 mm) arc height. The arc height of the
44、 Almen strip surface to be coated shall be measured after grit-blast surface preparation (first reading) and again after coating application (second reading). The first reading and subsequent coating application shall be with the convex surface of the Almen strip in the up position if the strip is n
45、ot flat after grit blast and the second reading with the same surface, now coated, in the up position. The Almen strip shall be restrained flat, in the transverse direction by four screws located as indicated in SAE J442 during coating deposition. The measured change in deflection of the Almen strip
46、 resulting from the application of the coating shall be reported as the difference of the two readings, second reading minus first reading, and is indicative of the desired compressive coating stresses if the sign of the difference is positive. Acceptable values for Almen type “N” strip arc heights
47、are positive 0.003 to 0.012 inches (0.075 to 0.30 mm) for a 0.005 inch (0.13 mm) thick coating. 3.6.6 The minimum finished coating thickness shall be 0.003 inch (0.076 mm). Areas on which the coating presence is optional shall be exempt from the minimum thickness requirement. 3.7 Test Methods 3.7.1
48、Bend Test Test panels shall be approximately 0.05 x 1 x 3 inches (1.3 x 25 x 76 mm) and shall be coated on one side to a thickness of 0.001 to 0.003 inch (0.025 to 0.076 mm). Panels shall be tested by being bent around a 0.5 inch (13 mm) diameter bar, with the coated surface on the outside of the be
49、nd, at a rate of approximately ten degrees per second. Panels shall be bent to obtain a 90 permanent set. 3.7.2 Bond Strength Test specimens shall be bar approximately 1 inch (25 mm) in diameter by 2 inches (51 mm) long and shall be coated to a thickness of 0.009 to 0.012 inch (0.2 to 0.3 mm). Specimens shall be prepared and tested in accordance with ASTM C 633. Adhesive only qualification tests shall be run under the same test conditions to verify int
