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MAT SCI 298 > Lecture 5 - Titanium Alloys > Flashcards

Lecture 5 - Titanium Alloys Flashcards

1
Q

What is CP-Ti?

A

commercial purity Ti

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2
Q

What is the crystal structure of beta-Ti?

A

bcc

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3
Q

What is the crystal structure of alpha-Ti?

A

hcp

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4
Q

What is the density of ti?

A

4.5 g/cm3 (low)

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5
Q

What is the melting temperature?

A

1668C

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6
Q

What is the boiling point?

A

3287C

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7
Q

What is the Young’s Modulus of Ti?

A

110GPa (low)

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8
Q

What are the four types of Ti alloys?

A

alpha
alpha + beta
beta meta stable
beta stable

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9
Q

Why are Ti alloys used?

A

good specific tensile strength at elevated temperatures
excellent corrosion resistance

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10
Q

What is the density of Ti-6Al-4V?

A

4.429 g/cc (lower than normal titanium)

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11
Q

Which type of titanium is used for medical grade?

A

Ti-6Al-4V, extra low interstitials

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12
Q

What does an increased amount of Al (alpha stabilizer) do?

A

increases beta transus

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13
Q

Which elements have a neutral effect on Ti?

A

Sn, Zr

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14
Q

Which elements have an alpha-stabilizing effect on Ti?

A

Al, O, N, C

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15
Q

Which elements have an beta-isomorphous effect on Ti?

A

Mo, V, Ta, Nb

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16
Q

Which elements have a beta-eutectoid effect on To?

A

Fe, Mn, Cr, Co, Ni, Cu, Si H

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17
Q

What are the Ti-Al-x alloys?

A

alpha and alpha + beta

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18
Q

What are the Ti-transition-metal-based?

A

beta meta stable and beta stable

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19
Q

Alpha alloys have a higher _____ than pure Ti

A

beta transus

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20
Q

Addition of oxygen can raise _______ 4x

A

yield strength

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21
Q

Al-Sn additions are effective ________________

A

strengtheners

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22
Q

___________ values for Ti alloys are 2x higher than that of Al alloys

A

Klc (plane strain fracture toughness)

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23
Q

What is a martensitic transformation?

A

diffusion-less solid-to-solid phase transitions

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24
Q

What is the angle needed to change BCC to HCP?

A

10.6 degrees

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25
Q

Which phase is diffusion slower in?

A

alpha phase (hcp)

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26
Q

What does diffusion affect in AM

A

elemental partition

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27
Q

How do O and Al differ for AM?

A

powders have higher O and lower Al

28
Q

What is the yield strength and ductility of AM Ti-6Al-4V?

A

yield strength is high, ductility is small

29
Q

What are the five strengthening mechanisms for L-PBF in Ti64?

A

phase
solid solute
dislocation
boundary
pores

30
Q

What happens to the tensile ductility when 90 degrees from build direction?

A

drops dramatically

31
Q

voids play a role in _________ of PBF Ti64

A

necking and fracture behavior

32
Q

Why are Ti alloys tough to print via L-PBF?

A

martensitic phase transformation during 3D printing

33
Q

What challenges remain difficult to overcome?

A

impurities and pores

34
Q

What does a majority of 3D printed Ti64 alloys have?

A

poor ductility

35
Q

where are the studies of corrosion resistance and biocompatibility at?

A

ongoing

36
Q

what limits aerospace applications for 3d printed Ti64 alloys?

A

elevated temperature properties (creep) and fatigue properties

37
Q

What is BCC?

A

body centered cubic

38
Q

What is FCC?

A

face centered cubic

39
Q

What is HCP?

A

hexagonal close packing

40
Q

What is unique about titanium phases?

A

multiple phases unlike steels

41
Q

How does beta Ti compare with alpha Ti?

A

more ductile (alpha-Ti is brittle)

42
Q

What are the properties of alpha + beta Ti?

A

mix of ductile and brittle

43
Q

How does Ti do in low temperatures?

A

very good tensile strength

44
Q

How does Ti compare in weight?

A

very light

45
Q

What does ELI mean?

A

extra low interstitials (low oxygen levels)

46
Q

What happens when you add too much Al?

A

creates brittle Ti3Al

47
Q

Why do you want the beta transition temperature as low as possible?

A

avoid brittle material when cooling

48
Q

What are the gamma and omega phases?

A

too brittle, shatter

49
Q

What does alpha-stabilizing and beta-stabilizing mean?

A

the more of these elements you add, the more alpha/beta there is

50
Q

What happens if you add too much beta-stabilizing elements?

A

heavier, lose corrosion resistance

51
Q

what is the downside to beta Ti Alloys?

A

not as ductile as alpha + beta

52
Q

What happens to the shear strength from beta to alpha?

A

introduces tan(10.6 degrees) = .187 shear strength (18.7%)

53
Q

Which structures have the best close packing?

A

FCC and HCP

54
Q

What shape has the best diffusivity?

A

BCC

55
Q

What the cooling rates for the three quenching processes from highest to lowest?

A

water quench, air cooled, furnace cooled

56
Q

What is the typical L-PBF cooling rate?

A

10^7 K/s

57
Q

Why does iron get into the L-PBF build?

A

chamber is made of iron

58
Q

Why is beta identified as pre-beta?

A

it used to be beta but now is alpha’

59
Q

Where are impurities Fe and V located?

A

beta lines

60
Q

higher energy input means what for V?

A

higher quenching rate, less time for V to diffuse

61
Q

What does heat treatment do to V?

A

helps break it up

62
Q

What happens to Ti when repeated heating and cooling?

A

twinning and dislocations

63
Q

How does L-PBF/SLM compare to EBM in properties?

A

more alpha than beta, higher cooling rate, more yield strength, less ductility

64
Q

What happens if you use an insufficient energy input on Ti?

A

reduce fatigue cycle

65
Q

What are the optimal temperatures for annealing Ti5553?

A

300 and 800C

MAT SCI 298 (11 decks)

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