TY - JOUR

T1 - In-situ fatigue in an environmental scanning electron microscope - Potential and current limitations

AU - Biallas, G.

AU - Maier, H. J.

N1 - Funding Information: Financial support by Deutsche Forschungsgemeinschaft is gratefully acknowledged.

PY - 2007/8

Y1 - 2007/8

N2 - The present study provides a survey on in situ fatigue devices suitable for loading specimens in a scanning electron microscope (SEM). Particular emphasis is placed on the experimental methods employed to operate a small-scale load frame in an environmental SEM (ESEM). Specimen design and surface preparation, various modes of conducting the fatigue tests, specimen heating and imaging at elevated temperatures are considered. In addition, recent data from in situ fatigue studies conducted in an ESEM between room temperature and 600 °C are summarized. Fatigue tests conducted on AM60B cast magnesium demonstrate a substantial environmental effect on cyclic deformation and fatigue damage evolution even at room temperature. Fatigue behaviour of high-temperature titanium alloy IMI 834 at 400 °C illustrates a completely different effect of environment on slip band formation and crack nucleation as compared to AM60B. Investigations performed on IMI 834 at 600 °C reveal current limitations of the in situ fatigue technique applied. An approach to overcome these limitations is discussed. Ambient conditions can be simulated in an ESEM using pure water vapour atmosphere at a pressure similar to the partial pressure of the ambient environment. This is demonstrated for AM60B at room temperature and IMI 834 at 400 °C. However, this approach cannot necessarily be applied to all other material/environment combinations as is exemplarily shown for in situ fatigue loading of IMI 834 at 600 °C. Data obtained from in situ fatigue testing are compared to those from post-mortem SEM studies of failed specimens, which portray a wrong impression in certain cases. Experimental issues specific to environmental in situ testing at elevated temperatures are addressed as are the ramifications of such tests with respect to modelling of fatigue life.

AB - The present study provides a survey on in situ fatigue devices suitable for loading specimens in a scanning electron microscope (SEM). Particular emphasis is placed on the experimental methods employed to operate a small-scale load frame in an environmental SEM (ESEM). Specimen design and surface preparation, various modes of conducting the fatigue tests, specimen heating and imaging at elevated temperatures are considered. In addition, recent data from in situ fatigue studies conducted in an ESEM between room temperature and 600 °C are summarized. Fatigue tests conducted on AM60B cast magnesium demonstrate a substantial environmental effect on cyclic deformation and fatigue damage evolution even at room temperature. Fatigue behaviour of high-temperature titanium alloy IMI 834 at 400 °C illustrates a completely different effect of environment on slip band formation and crack nucleation as compared to AM60B. Investigations performed on IMI 834 at 600 °C reveal current limitations of the in situ fatigue technique applied. An approach to overcome these limitations is discussed. Ambient conditions can be simulated in an ESEM using pure water vapour atmosphere at a pressure similar to the partial pressure of the ambient environment. This is demonstrated for AM60B at room temperature and IMI 834 at 400 °C. However, this approach cannot necessarily be applied to all other material/environment combinations as is exemplarily shown for in situ fatigue loading of IMI 834 at 600 °C. Data obtained from in situ fatigue testing are compared to those from post-mortem SEM studies of failed specimens, which portray a wrong impression in certain cases. Experimental issues specific to environmental in situ testing at elevated temperatures are addressed as are the ramifications of such tests with respect to modelling of fatigue life.

KW - AM60B

KW - Cast magnesium

KW - Crack initiation

KW - Damage evolution

KW - Environmental degradation

KW - Fatigue mechanisms

KW - High-temperature titanium alloy

KW - IMI 834

KW - In situ fatigue

KW - Microstructure

KW - Small crack growth

UR - http://www.scopus.com/inward/record.url?scp=33947653270&partnerID=8YFLogxK

U2 - 10.1016/j.ijfatigue.2006.11.008

DO - 10.1016/j.ijfatigue.2006.11.008

M3 - Article

AN - SCOPUS:33947653270

VL - 29

SP - 1413

EP - 1425

JO - International journal of fatigue

JF - International journal of fatigue

SN - 0142-1123

IS - 8

ER -