FATIGUE MECHANISMS IN P/M COMPONENTS Worcester Polytechnic - - PowerPoint PPT Presentation

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FATIGUE MECHANISMS IN P/M COMPONENTS Worcester Polytechnic - - PowerPoint PPT Presentation

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FATIGUE MECHANISMS IN P/M COMPONENTS Worcester Polytechnic Institute October 27-28, 2004 Diana Lados & Diran Apelian M orris B oorky P owder M etallurgy R esearch C enter OUTLINE I. Impact of Porosity and Microstructure on Fatigue

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SLIDE 1

FATIGUE MECHANISMS IN P/M COMPONENTS

Worcester Polytechnic Institute October 27-28, 2004

Diana Lados & Diran Apelian

Morris Boorky Powder Metallurgy Research Center

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SLIDE 2

OUTLINE

  • I. Impact of Porosity and Microstructure on Fatigue

and Fatigue Crack Growth Behavior of P/M Components (examples from the literature)

  • Effects of porosity
  • Effects of microstructure
  • II. WPI project … Objectives and Experimental Plan
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SLIDE 3

BACKGROUND

Factors controlling fatigue behavior …

1. Porosity:

  • Amount (% Porosity)
  • Type (Open/Closed)
  • Morphology/Distribution (influenced by sintering

conditions and initial powder type/morphology)

2. Microstructure:

  • Transition from pore-control (low density) to

microstructure-control (high density)

  • Homogeneous vs. Heterogeneous

(pre-alloyed vs. admixed)

  • Phase/Amount of phase (Martensite, Bainite, Pearlite,

Ni-rich areas, etc.)

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SLIDE 4

BACKGROUND

Fatigue life vs. density/porosity … pore amount

Fatigue limit Porosity %

for both:

P/M iron P/M steels

in:

as-sintered heat treated (quench and tempered)

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SLIDE 5

BACKGROUND

Fatigue life vs. density/porosity … pore amount Fe-1.75Ni-1.5Cu-0.5Mo-0.6C Fe-2Cu-0.8C

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SLIDE 6

BACKGROUND

Fatigue life vs. density/porosity … pore amount Fe-2Cu-2.5Ni

(60 min @ 2280°F)

Fe-1.5Cu-0.6C

(30 min @ 2050°F)

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SLIDE 7

BACKGROUND

Fatigue life vs. density/porosity … pore type

The effect of porosity type (open vs. closed) for a given density has not been reported in the literature ?????

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SLIDE 8

BACKGROUND

Fatigue life vs. density/porosity … pore morphology

20 min @ 2050°F 30 min @ 2340°F 2340ºF 2192ºF

Fe-1.5Mo-0.7C

Pre-alloyed Admixed

ABC (atomized) MH (sponge) Fe- 1.75Ni-1.5Cu-0.5Mo-0.5C (SE) Fe- 4Ni-1.5Cu-0.5Mo-0.5C (AE)

and

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SLIDE 9

BACKGROUND

Fatigue life vs. density/porosity … pore morphology

2050ºF 2282ºF 2050ºF 2340ºF Fe-1.75Ni-1.5Cu- 0.5Mo-0.5C Fe-4Ni-1.5Cu- 0.5Mo-0.5C

Fe-4Ni-1.5Cu-0.5Mo

(diffusion alloyed )

S based on sponge Fe powder A based on atomized Fe powder

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SLIDE 10

BACKGROUND

Fatigue life vs. microstructure … pore-control vs. microstructure-control With increasing density the differences between the strain life curves become larger Decreasing porosity increases microstructural influence on fatigue life Fe-1.75Ni-0.5Mo

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SLIDE 11

BACKGROUND

Fatigue life vs. microstructure … pore-control vs. microstructure-control Higher density Enhanced resistance to fatigue crack growth Uniform shifts Density/porosity dominates FCGR over the microstructure of the matrix Fe-1.75Ni-0.5Mo-0.5C

(homogeneous - divorced pearlite)

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SLIDE 12

BACKGROUND

Fatigue life vs. microstructure … homogeneous (pre-alloyed) vs. heterogeneous (admixed)

∆K, MPa m1/2

Homogeneous structure better fatigue crack growth resistance than inhomogeneous structure

(different as-sintered microstructures for the homogeneous (divorced pearlite) and inhomogeneous (ferrite, pearlite, and martensite)

Fe-1.75Ni-0.5Mo-0.5C

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SLIDE 13

BACKGROUND

Fatigue life vs. microstructure … homogeneous (pre-alloyed) vs. heterogeneous (admixed)

Pre-alloyed Admixed Partially alloyed

Different as-sintered microstructures:

Pre-alloyed: martensite Partially alloyed: pearlite + Ni-rich ferrite, martensite, Ni-rich areas Admixed: pearlite + Ni-rich ferrite, martensite, Ni-rich areas

Fe-4Ni-1.5Cu-0.5Mo-0.5C

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SLIDE 14

BACKGROUND

Fatigue life vs. microstructure … heterogeneous 1 (diffusion alloyed) vs. heterogeneous 2 (binder treated)

  • no significant difference

between diffusion alloyed and binder treated Diffusion alloyed Binder treated

Fe-1.75Ni-1.5Cu-0.5Mo-0.6C

(divorced pearlite, martensite, and Ni-rich ferrite )

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SLIDE 15

BACKGROUND

Fatigue life vs. microstructure … microstructure 1 vs. microstructure 2 High cooling rate: finer pearlite + more martensite + bainite Slow cooling rate: pearlite + martensite + bainite Fe-4Ni-1.5Cu-1.5Mo-0.8C

(diffusion alloyed )

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SLIDE 16

OBJECTIVES

  • Study the effects of density/porosity on the fatigue

initiation and propagation in P/M components;

  • Investigate the porosity/microstructure interactions;
  • Understand the effects of microstructural homogeneity and

microstructural phases on dynamic properties – mechanisms;

  • Create guidelines for fatigue design corroborated with the

fundamental understanding of the alloys behavior;

  • Optimize the material characteristics and processing

parameters for enhanced fatigue response.

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SLIDE 17

EXPERIMENTAL APPROACH

Materials selection … Pre-alloyed (QMP ATOMET 4601 Ni-Mo pre-alloyed powder) Admixed (hybrid) (QMP ATOMET 4001 Mo pre-alloyed powder admixed with Ni) 0.65 0.15-0.18 0.50-0.55 1.75-1.8

[%] Sintered C Mn Mo Ni Chemical composition

Graphite Ni Graphite

Molding grades particles (70-85 µm)

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SLIDE 18

EXPERIMENTAL APPROACH

Project phases … Phase I (a): Phase I (a): Effects of porosity amount on fatigue behavior; Phase I (b): Phase I (b): Microstructural effects on fatigue response; Phase II: Phase II: Effects of porosity type & morphology (size/shape)

  • n fatigue.

Is fatigue resistance a state function ???

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SLIDE 19

BACKGROUND

Total porosity …

Open porosity Isolated porosity Closed porosity

Total Porosity: Open + Closed + Isolated

Open porosity: continuous pore channels intersecting the surface of the specimen (and each other) Closed porosity: closed gaps between powder particles resulting from compaction and/or sintering (not accessible to the surface BUT can be connected to each other !!) Isolated porosity: pores present in the initial powder particles (not affected by compaction and sintering)

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SLIDE 20

EXPERIMENTAL APPROACH

Phase I … Porosity considerations Micro- structure Set 3 7.83 Set 2 ~7.2 Set 1 ~6.9 Density [g/cm3]

  • 3 “total porosity” levels (total porosity is

measured from geometry/weight data)

  • Pores of the same type (open) and similar

morphology for both pre-alloyed and admixed

Porosity amount amount is studied

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SLIDE 21

EXPERIMENTAL APPROACH

Open porosity measurement techniques …

Open porosity penetrated by He Isolated porosity Closed porosity Open porosity penetrated by oil Open porosity unresolved by penetrating oil

Oil-impregnation

(ASTM B328)

Gas-impregnation

More accurate measurements of

  • pen porosity due to increased

pore penetration ability of gases compared to oils - RECOMMENDED Calculate the interconnected porosity from the volume of oil that has impregnated the specimen - OVERESTIMATIONS

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SLIDE 22

EXPERIMENTAL APPROACH

Gas-impregnation measurement techniques … pycnometry Gas displacement pycnometer: a sample of known weight (a solid, a powder, or a porous material) is placed in one of the chambers and the change in pressure needed to balance the two chambers is used to calculate the volume of the sample (P1V1=P2V2) pore free density pycnometric density bulk density

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SLIDE 23

EXPERIMENTAL APPROACH

Calculation of open/closed porosity using He pycnometry …

free pore bulk total

1 V

−

ρ ρ − = % Total porosity = 100 x Vtotal

c pycnometri bulk

  • pen

1 V ρ ρ − =

% Open porosity = 100 x Vopen Vclosed = Vtotal – Vopen % Closed porosity = 100 x Vclosed

* The amount of isolated porosity was assumed insignificantly small

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SLIDE 24

EXPERIMENTAL APPROACH

Phase I … Porosity/density considerations Micro- structure Set 3 7.83 Set 2 ~7.2 Set 1 ~6.9 Density [g/cm3]

  • 3 “total porosity” levels (total porosity is

measured from geometry/weight data)

  • Pores of the same type (open) and similar

shape factor for both pre-alloyed and admixed

Porosity amount amount is studied

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SLIDE 25

EXPERIMENTAL APPROACH

  • Compaction:
  • low densities (Set 1): normal compaction;

↔ intermediate densities (Set 2): controlled temperature compaction (warm compaction 145°F );

  • high densities (Set 3): powder forging.
  • Sintering:

temperature:T=2050°F ;

  • time: t=30 min;

T and t invariant for phase I. Phase I … Compaction + Sintering

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SLIDE 26

EXPERIMENTAL APPROACH

Open/closed porosity results using He pycnometry …

Sintered conditions 0.25 0.5 0.75 1 1.25 6.8 6.9 7 7.1 7.2 7.3 7.4 Density (g/cm3) Closed porosity (%)

A4601 A4001

Pre-alloyed Admixed

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SLIDE 27

EXPERIMENTAL APPROACH

Phase I … Microstructural considerations

III. ? ?

Cooling Fatigue rate (L) behavior (L) Cooling Fatigue rate (H) behavior (H) Microstructure 1 Microstructure 2

? ?

Powder Fatigue type (2) behavior (2) Powder Fatigue type (1) behavior (1) Pre-alloyed

(homogeneous)

Admixed

(heterogeneous)

Low density High density

I.

Pore control Pore/Matrix control Matrix control

II.

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SLIDE 28

EXPERIMENTAL APPROACH

Phase I … Heat treatment

  • Post sintering heat treatment:

austenitize @ 1700°F for 30 min (similar austenitic grains) No-oil quench to 2 microstructures (for both pre-alloyed and admixed): temper @ 400°F for 1 hr (similar matrix micro-hardness) Martensite + (5% Ni reach areas) 40%Martensite + 60%Pearlite + (~5% Ni reach areas)

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SLIDE 29

EXPERIMENTAL APPROACH

Phase I … Heat treatment 1 … High bar He quench 100% Martensite 90-95% Martensite (5% Ni reach areas)

6 bar He quench (~9.9 ºF/sec) 7 bar He quench (~11.7 ºF/sec) 10 bar He quench (cooling rate close to oil quench <20 ºF/sec)

Pre-alloyed Admixed

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SLIDE 30

EXPERIMENTAL APPROACH

Phase I … Heat treatment 2 … sinter hardening … cooling rates

A4601 + 0.6% C at 7.00 g/cm3

Continuous Sinter Cooling Transformation Diagram

100 200 300 400 500 600 700 800 900 1000 0.0 5.0 10.0 15.0 20.0 25.0

Time (minutes) Temperature oC

196 oC/min 106 oC/min 87 oC/min 35 oC/min

A F + C

  • C/min

% % % % R/A 196

  • 91

9

  • 54

151

  • 76

24

  • 53

106

  • 79

21

  • 52

107

  • 69

31

  • 50

87

  • 53

47

  • 49

60

  • 35

65

  • 47

35

  • 20

80

  • 47

Ferrite

Microstructure & Apparent Hardness

Ave Cooling Rate Martensite Fine Pearlite Divorced Eutectoid Apparent Hardness

~1.1 ºF/sec ~2.6 ºF/sec ~3.2 ºF/sec ~5.9 ºF/sec

Pre-alloyed

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SLIDE 31

EXPERIMENTAL APPROACH

Phase I … Heat treatment 2 … sinter hardening … microstructures

Pre-alloyed

~5.9 ºF/sec ~1.8 ºF/sec

Fine Pearlite + small islands of Divorced Eutectoid Divorced Eutectoid (with

Widmanstätten-like carbides) + Pearlite

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SLIDE 32

EXPERIMENTAL APPROACH

Phase I … Heat treatment 2 … sinter hardening … cooling rates

A4001 + 1.8% Ni + 0.6% C at 7.00 g/cm3

Continuous Sinter Cooling Transformation Diagram

100 200 300 400 500 600 700 800 900 1000 0.0 5.0 10.0 15.0 20.0 25.0

Time (minutes) Temperature oC

196 oC/min 106 oC/min 87 oC/min 35 oC/min

A A + F + C M + F + C F + C

60 oC/min

  • C/min

% % % % R/A 196 16.2 1.3 73 9 58 149 16.3 1.5 64 18 55 106 7.9 2.1 68 23 55 107 7.1 3.1 62 28 54 87 6.2 1.8 55 37 52 59 6.3 1.8 50 42 51 35 2.6 1.0 46 51 50 Microstructure & Apparent Hardness

Ave Cooling Rate Nickel Rich Martensite Nickel Rich Area Fine Pearlite Divorced Eutectoid Apparent Hardness

~1.1 ºF/sec ~5.9 ºF/sec ~1.8 ºF/sec ~2.6 ºF/sec ~3.2 ºF/sec

Admixed

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SLIDE 33

EXPERIMENTAL APPROACH

Phase I … Heat treatment 2 … sinter hardening … microstructures

Admixed

~5.9 ºF/sec ~1.8 ºF/sec

Fine Pearlite + Martensite + small islands of Divorced Eutectoid Divorced Eutectoid + Pearlite + Martensite

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SLIDE 34

EXPERIMENTAL APPROACH

Phase I … Heat treatment 2 … Low bar He quench

3 bar He quench (~7.4 ºF/sec) 2 bar He quench (~6.1 ºF/sec) <1 bar He quench

100% Martensite 40% Martensite + 60% Pearlite (with Divorced Eutectoid) (5% Ni reach areas)

Pre-alloyed Admixed

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SLIDE 35

EXPERIMENTAL APPROACH

Phase II … Is Fatigue Resistance a State Function ?

One density level is selected (~7.2 g/cm3, same as Set 2 in Phase I) and 5 ways of achieving are investigated in parallel (for both pre-alloyed and admixed materials):

1. Compaction and regular sintering for molding grade particles, 70-85 µm (Phase I, Set 2); 2. Compaction and regular sintering for finer powders, ~50 µm; 3. Normal compaction to 7.0 g/cm3, followed by a high-temp./long time sinter; 4. Normal compaction to 7.0 g/cm3, followed by a low-temp./long time sinter; 5. Double press/Double sinter (same closed porosity as 2).

Pore size/shape & type effects on the fatigue behavior

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SLIDE 36

EXPERIMENTAL APPROACH

Phase II … Various pore sizes/shapes/types

Pore type Pore morphology (size/shape) Case study Open / irregular Open / round Closed / round Open / irregular / smaller Open / irregular

  • 5. DP/DS

(1550ºF/ 30min + 2050ºF/ 30 min

  • 4. Comp. and

low temp /long time sintering (TBD)

  • 3. Comp. and

high temp /long time sintering (2350ºF/6hrs)

  • 2. Comp. and

regular sinter (2050ºF/30min) for finer powders (~50 µm)

  • 1. Comp. and

regular sinter (2050ºF/30min) for molding grade powder (70-85 µm)

  • Fatigue and fatigue crack growth tests will be conducted

for both powders and one microstructure

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SLIDE 37

EXPERIMENTAL APPROACH

Phase II … Porosity type

1 2 3 4 5 6 7 6.8 6.9 7 7.1 7.2 7.3 7.4 Density (g/cm3) Closed porosity (%)

Single press and sinter High temperature-long time sintering Double press-double sinter

HTS SPS DP/DS

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SLIDE 38

EXPERIMENTAL APPROACH

Phase II … Pore morphology

HTS

10 20 30 40 50 60 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Shape Factor Frequency (% of Total)

87% Closed Porosity

SPS DP/DS

5 10 15 20 25 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Shape Factor Frequency (% of Total)

2.5% Closed Porosity

5 10 15 20 25 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Shape Factor Frequency (% of Total)

10% Closed Porosity

2 4 6 8 10 12 14 16 18 1 2 3 4 5 Aspect Ratio l/w Frequency (% of Total)

2.5% Closed Porosity

2 4 6 8 10 12 14 16 18 1 2 3 4 5 Aspect Ratio l/w Frequency (% of Total)

10% Closed Porosity

5 10 15 20 25 1 2 3 4 5 Aspect Ratio l/w Frequency (% of Total)

87% Closed Porosity

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SLIDE 39

EXPERIMENTAL APPROACH

Fatigue and fatigue crack growth testing … Specimens

1.56” 0.3125” Dia 0.45” Dia 0.25” 3.5” 0.75” 1.5”

C(T) specimens for fatigue crack growth testing Dog-bone specimens for strain-control fatigue testing

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SLIDE 40

EXPERIMENTAL APPROACH

Fatigue and fatigue crack growth testing … Tests conducted by the WPI team in collaboration with Fracture Technology Associates (Mr. Keith Donald); *1 sample for each of the 20 conditions [pre-alloyed+admixed, 3 density levels, 2 microstructures (12) + pre-alloyed+admixed, 1 density (7.2 g/cc), 2 microstructures (8)] Tests done at The Royal Military College of Canada (Dr. David DuQuesnay); *3 failed samples at 4 life levels for each of the 20 conditions):

* 103-104 * 104-105 * 105-106 * 106-107

  • 2. Fatigue crack growth

tests (E647)

  • 1. Strain-control fatigue

tests (E 606)

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SLIDE 41

FUTURE WORK …

  • Finalize the heat treatment study and select the “bar quenches” for

all four conditions (two powders and two microstructures);

  • Do a low temperature/long time sintering study to ensure

the condition of open porosity with high shape factor;

  • Perform static tensile tests to get YS, Young’s modulus, UTS for all

cases (80 samples);

  • Check the residual stress level and decide if an additional stress

relieving is needed after the post-sintering heat treatment;

  • Prepare samples for the life study (240 dog-bone samples) and the

fatigue crack growth testing (20 compact tension specimens);

  • Machine all the samples;
  • Start fatigue and fatigue crack growth work.
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SLIDE 42

TEAM WORK …

QMP (Canada) Hoeganaes Corp. (USA) Metaldyne (USA) NA Höganäs (USA) Höganäs AB (Sweden) Solar Atmospheres (USA) Fracture Technology Assoc. (USA) Royal Military College (Canada) WPI (USA) Consortium Members