1. Chemical mixing forced by plastic deformation: a new analysis by analogy with mixing in fluid flows

MECHANICAL MIXING IN METALLIC ALLOYS DURING BALL MILLING AND SLIDING WEAR

Pascal Bellon, University of Illinois, DMR Award# 0304942

• We extended the analysis of mixing of passive markers by turbulent fluid flows to the mixing of chemical species in alloys subjected to sustained plastic deformation (collab. R.S. Averback, UIUC)

• Dimensional analysis and full analytic solution show that mixing is superdiffusive and increases with the scale of the features considered (manuscript in preparation)

• We are currently applying this analysis to explain the dynamical stabilization of compositional patterns

Dif

fusi

on c

oeff

icie

nt

Feature scale

Dshear

|Dth|

p

- At short scale |Dth | > Dshear decomposed

- At large scale |Dth | < Dshear mixed

- Scale of pattern |Dth | ≈ Dshear

Thus

pattern scale p Lbox Dth

bsh

Scale-dependent shear mixing provides a direct explanation of compositional

patterning induced by plastic deformation

-by 3D atom probe tomography (collab. D.N. Seidman, Northwestern Univ.)

Cu-Ag nanocomposite

-by kinetic Monte Carlo simulations

(100) cut of a nanocomposite

2. Broader impacts:

MECHANICAL MIXING IN METALLIC ALLOYS DURING BALL MILLING AND SLIDING WEAR

Pascal Bellon, University of Illinois, DMR Award# 0304942

2 undergraduate students Active-learning teaching methodhave joined this research program

• Alicia Kuhl and David Narbutas, junior from MSE-UIUC, have joined our group since Jan. 2005, worked this summer as research assistants (REU program), and continue this fall. They have been trained to pin-on-disc wear testing, XRD and SEM characterization (see picture below), and kinetic Monte Carlo simulations.

• Implementation and evaluation of an active-learning teaching method in Metals senior courses taught by PI at MSE-UIUC

-Very positive feedback from students through survey

- PI cited on the list of teachers ranked as excellent by their students (spring 2005)

- PI served as classroom observer for new faculty in College of Engineering

- PI selected for classroom visits by new Engineering faculty (FastStart program)

II. Wear Rate Transition During Dry Sliding of Cu-15Ni-8Sn Spinodal Alloy

MECHANICAL MIXING IN METALLIC ALLOYS DURING BALL MILLING AND SLIDING WEAR

Pascal Bellon, University of Illinois, DMR Award# 0304942

Mixing during sliding wear

• Identification of mild to severe wear regime as load increases and as sliding distance increases.

• Preliminary results (XRD) suggest that intense plastic deformation in transfer layer lead to disappearance of spinodal structure to benefit of FCC solid solution. The resulting softening may account for wear regime transition.

Fig. 2: Wear volume (mm3) during dry sliding of Cu-Ni-Sn pin on SS 440C disc at room temperature.

Note the transition from mild to severe wear for 3 kg load at ≈1000m.

III. Broader Impacts

• Training of one REU (Jason Bares, University of Wisconsin-Madison) on wear and materials characterization.

• Implementation of an active-learning method to teach course on “Design of Engineering Alloys” in spring 2004.

Fig. 3: X-ray diffractograms of

(a) initial spinodally decomposed (SD) alloy – see red arrows,

(b) wear debris collected in severe wear regime. XRD indicative of fcc solid solution without SD.

(a) (b)