Titanium

Question 1

What are the main ores used in Titatium Production?

Answer 1

• Ilmenite
• Rutile

Question 2

Phase Transformation

Answer 2

Change in crystallographic arrangement of atoms at higher temperatures

Question 3

When does phase transformation happen for Pure titanium?

Answer 3

882^oC

HCP ► BCC

Question 4

What is a phase?

Answer 4

Any part of a material with a distinct crystal structure and/or chemical composition

Question 5

What are the 2 designation off Ti alloys and what do they mean?

Answer 5

1. Alpha- alloying elements act to stabilise hexagonal alpha phase
2. Beda- alloying elements act to stabilise BCC beta phase

Question 6

Alpha stabilsing elements are

Answer 6

Al, Sn, Zr and O

Question 7

Beta stabilising elements are

Answer 7

Mo, V, Cr and Nb

Question 8

What is the strongest Alpha staibilser?

Answer 8

Al. Dissolves in the Ti matrix and acts as a strengthening agent up to 550^oC

Question 9

What happens when you increase the amount of alpha stabilsers?

Answer 9

Increase in transfromation temperature between alpha and beta phase

Question 10

What do Beta stabilisers do?

Answer 10

• Lower the beta transus temp.
• Provide solid solution strengthening by preferentially dissolving in the beta phase

Question 11

What are the 2 categories of beta stabilisers?

Answer 11

• Isomorphous- Alloying element and beta phase mutually soluble (V, Mo)
• Eutecoids- Soild state reaction in which 2 new phases are precipated over a range of compositions (Fe, Mn, Cr)

Question 12

What are (alpha+beta) systems?

Answer 12

Contain both types of stabilising elements below levels where detrimental phases form

Question 13

What is the Kroll Process?

Answer 13

1. Chlorination of the ore to TiCl₄
2. Purification of TiCl₄
3. Reduction of TiCl₄ to Ti sponge
4. Processing of sponge

Question 14

How is Ti melted?

Answer 14

Electrode arc melting under vacuum (VAR) - Compacts are formed from ti granules and alloying elements then welded together

Question 15

Problems with VAR?

Answer 15

1. Random occurence of high density- From contamination of raw materials
2. Random occurence of hard alpha inculsions- From high concentrations of interstitial alpha stabilsers

Question 16

How to over come VAR problems?

Answer 16

Cold Hearth process

Question 17

What furnaces are available for cold hearth processes?

Answer 17

• Electron beam
• Plasma torch

Both reduce and even eliminate defect population

Question 18

Disadvantage of Cold hearth process?

Answer 18

Less efficent in terms of melting capability.

• EB- loses in high vapour pressure elements
• Plasma- Less effective hydrogen removal

Question 19

How does a cold hearth process work?

Answer 19

1. Raw material enter a water cooled copper hearth at one end where they are melted by electrom beam or plasma
2. Heating is maintained and HDI and hard alpha particles get trapped in skull
3. Molten metal then moves to a cooled copper mold and become an ingot

Question 20

Slow Cooling rate (air or furnace cool) in heat treatment leads to

Answer 20

Nucleation and diffusion of atoms- widmanstattan microstructure

Question 21

Fast cooling rates leads to

Answer 21

hexagonal alpha- needle like form