Masters Theses

Keywords and Phrases



"The application of friction stir spot welding (FSSW) for joining advanced high strength steel (AHSS) offers improvements in automobile fuel economy and crashworthiness. FSSW is a solid-state process and therefore bypasses liquid phases that form during conventional resistance spot welding. This process eliminates detrimental solidification weld defects such as cracking and debonding.

A hybrid hi-material FSSW tool comprised of cobalt-cemented tungsten carbide (WC-Co) was bonded to a tungsten-nickel-iron heavy alloy (WHA). A unique sinterbonding process was used to bond the two materials. Sinterbonding WC-Co powder to WHA, using hot pressing to apply pressure, resulted in an ideal consolidated interface. Thermodynamic analyses showed cobalt-rich eta-phase carbides are favored to form at the interface due to a reduction in carbon activity.

The mechanical performance of FSSW welds on various AHSS was evaluated. For constant FSSW parameters, martensitic AHSS (M190) did not result in higher lap shear strengths (LSS) compared to dual phase AHSS (DP 590) which has less than half the tensile strength M190. The results suggest that higher strength materials are more resistant to material flow under the tool during welding, which results in smaller bonded regions and LSS.

The formation of a strength-reducing soft ferrite layer originating from the sheet faying surfaces was investigated for a martensitic AHSS. A series of welds with varying process times (i.e., varying total energy input) was performed to investigate welding parameter effects on the ferritic layer formation. For the conditions explored, the extent of ferrite formation was dependent on oxygen availability"--Abstract, page iv.


Mishra, Rajiv S.

Committee Member(s)

Hilmas, Greg
Miller, F. Scott, 1956-


Materials Science and Engineering

Degree Name

M.S. in Materials Science and Engineering


Missouri University of Science and Technology. Intelligent Systems Center

Research Center/Lab(s)

Intelligent Systems Center


Missouri University of Science and Technology

Publication Date

Fall 2008

Journal article titles appearing in thesis/dissertation

  • Sinterbonding cobalt-cemented tungsten carbide to tungsten heavy alloys
  • Mechanical evaluation of friction stir spot welded advanced high strength steels
  • Ferrite layer formation at faying surface during friction stir spot welding of martensitic steels


x, 71 pages

Note about bibliography

Includes bibliographical references.


© 2008 Jeffrey Michael Rodelas, All rights reserved.

Document Type

Thesis - Restricted Access

File Type




Subject Headings

Friction stir welding
Steel, High strength

Thesis Number

T 9443

Print OCLC #


Electronic OCLC #


Link to Catalog Record

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