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MONASH UNIVERSITY

Department of Materials Engineering


SURFACE COATINGS EXPERIMENT P50


AIM


This experiment is designed to introduce you to two widely-used processes for the production of surface coatings with useful engineering properties on the surfaces of components.


REFERENCES


K.G. Budinski, ‘Surface Engineering for Wear Resistance’, Ch. 3, Prentice-Hall, Englewood Cliffs, New Jersey (1987).


ASM Metals Handbook, Vol. 18, ‘Friction, Lubrication and Wear Technology’, ASM International, Metals Park, Ohio, (1992), pp. 834-839.


ASM Metals Handbook, Vol. 5, ‘Surface Cleaning, Finishing and Coating, ASM, Metals park, Ohio, 9th ed. (1982).


INTRODUCTION


The work is to be performed and written up during the laboratory session. At the end, you should hand in the work sheet (attached) to your demonstrator.


The two coatings to be studied are Hard Chromium Plating and Electroless Nickel Plating. The objective is to understand how these two processes work, the properties of the coatings that they produce and the applications for which they are likely to be suitable.


Specimens


Two steel plates are provided for each of the surface treatments. One of them is in the ‘as plated’ condition while the other has been heated (in air) in a laboratory furnace at 400˚C for one hour. To save time (and trouble) a piece has been cut out of each plate and mounted edge-on for metallographic examination. The section that you can examine includes the edge of the original plate. The four resulting specimens are labelled as follows:


Cr1 - Hard Chromium plated

Cr2 - Hard Chromium plated and heated 1 hour at 400˚C

Ni1 - Electroless Nickel plated

Ni2 - Electroless Nickel plated and heated 1 hour at 400˚C


Information


If we have not yet discussed these processes in lectures, you will need some information before you start thinking about them. Attached are copies of extracts from ASM Metals Handbook, Desk Edition, describing the processes. These are condensations of the relevant chapters from the full ASM Metals Handbook Volume 5, ‘Surface Cleaning, Finishing and Coating’, 9th edition. Copies of the complete chapters are also available for your reference when you are seeking answers to the questions below - these copies are not to be removed from the laboratory.


Also available are the advertising leaflets published by the company that provided the specimens for us - Hardchrome Engineering Pty. Ltd.


EXPERIMENTAL PROCEDURE


Wear safety glasses and gloves.


If you spill etchant on your skin, wash the area thoroughly with cold water.


While each of you is required to hand in a completed work sheet, you are expected to work cooperatively in preparing specimens and making measurements. The idea is to learn as much as you can about these coatings by observation of the surfaces and the cross-sections, which you will have to polish and etch. The microhardness tester is available for hardness and thickness measurements on the cross section.


REPORT


The Work Sheet has to be handed in at the end of the laboratory session.


ASSESSMENT


Assessment will be based on the work sheet submitted. The mark (out of 20) will contribute 3% to the total mark for the subject.


WORK SHEET NAME: ........................................................



Hard Chromium

The Cr has been deposited from a high concentration sulphate bath.

Hardness of coating:

As plated


Heat treated





Thickness of coating:





Microstructure of cross-section:

As plated


Heat treated

(any change)




Observation of surface (can you see any cracks?)




What are the advantages and disadvantages of having micro-cracking in chromium deposits?





WORK SHEET NAME: ........................................................



Electroless Ni plating

.

Hardness of coating:

As plated


Heat treated





Thickness of coating:





Microstructure of cross-section:

As plated


Heat treated

(any change)




Observation of surface (can you see any cracks?)




What are the advantages and disadvantages of electroless nickel plating vs hard chromium plating?






April, 2007

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