After polishing try by pressing in hydraulic press, keep the material  between glass sheets.

i suppose the material is a soft one.

pl mention hardness

good advice! i should have a try.  i didn't have to test the hardness cause these were not structural materials. but i'm sure the low-tin samples are slightly harder than pure copper whose hardness is supposed to be around 40 HB.

when polished, the samples were mirror-like, after etched, scratches were evident.

Dear

Domgsheng Wen,

Are the scratches visible to naked eye after etching? If yes then the problem most likely is that there is too much dissolution of some component of the metal. try by reducing etching time or using a milder etchant.

dear

Pramod Vadavkar,

Those scratches were not visible to naked eye, but quite evident under 100x optical microscope, more evident than grain or phase boundaries. The etchant I used was 5g FeCl3+10ml HCl+100ml H2O, etching time several minutes.

dear 

Pramod Vadavkar,

sorry for the mistake: etching time several seconds!

Take care to clean your sample very, very well between each polishing step. Ultrasonic bath is a good solution.

The final polishing should be may be electrolytic ?

Dear Albert Cerri,

thank you! I did use ultrasonic bath between 2000-grit paper, 1.5W  and 0.5W grinding paste polishing. I did not try electrolytic polishing and am willing to try.

any electrolytic suggestions? i don't have experience on this

Some additional questions :

- Are you sure that your alloy is clean and does not contains any oxides ?

- Did you melt in vacuum or with gas protection ?

- Did you look at the surface of your samples after eachpolishing step ? ahaow do they scrachtes evolves ? Do they follow the average size of the grinding paper/paste or do they have always the same width?

To choose the right electrolyt : there are books about metallographic sample preparations. If you have a connection with somebody working with electron microscopy (TEM) go and ask them. In these books there is normally a list of alloys and the corresponding chemistry / voltage to be used.

We can discuss more ...

When I was young and fighting with this kind of problems I learned a lot from :

Practical Metallography [Jahresabo]

Zeitschriften-Abonnement Carl Hanser Verlag GmbH & Co. KG

How big are your samples ? What o you want do study with them ?

"The last step was polishing without any paste."  What is the point of that?  It is like trying to sand a board with the backside of the sandpaper.  Try one of these instead...

http://www.georgevandervoort.com/

Dear Alberto Cerri,

Greatly thank you for your questions, I looked back to find the answer for those questions:

-My alloy does not contain oxides because the samples were sintered using protective gas (5%H2+95%N2)

-I looked closely at the surface after every step and made sure the scratches were having the same width and in the same direction.

I really thank you for the book you recommended and I am looking for answers in it.

The samples are of 3mm x Φ14mm and they are prepared as simulated ancient bronzes.

Dear Richard Chinn, 

Thank you for your detailed answers! I think I will find my answers in the handbooks you listed. And I will try your advice according to the equipments and resources available. 

The handbook about polishing cloths will help me a lot! 

The fig.1 and 2 shows the sample before and after etched, respectively. The sample is Cu-10Sn-5Pb bronze alloy and polished using 0.5W diamond paste on polishing cloth. Fig.1 shows the scratches have only one direction (vertical), but fig.2 shows etched sample has two-direction scratches. Why I couldn’t see the second direction in fig.1? I used ultrasonic bath after every polishing step and make sure scratches were of one direction

this is fig.2

I see scratches in only direction in Figure 2.  Are you mistaking the many twin boundaries for scratches?  The twin boundaries are highly aligned, which probably indicates a preferred orientation, such as a rolling direction.  There are a few transverse scratches in both images.  The final polishing step I suggested in (3.) above would diminish all the scratches significantly.

Dear Richard Chinn,

Thank you very much, sir! I have followed your suggestion and eliminated the scratches! I have learned a lot!