Fracture failure analysis of shift pawl made by powder metallurgy
ZHAO Hongli1，WU Mei2，WANG Yuanhao1，LUO Cheng1
1School of Materials Science and Engineering，Hubei University of Automotive Technology，Shiyan 442002，
China；2School of Materials Science and Engineering，Hefei University of Technology，Hefei 230009，China
Abstract：The failure analysis of the shift pawl was carried out by the analysis of the macroscopic and microscopic
fracture morphologies as well as metallographic structure，hardness distribution and tightness. The results show
that the load of shift pawl is mainly caused by the reverse inversion of ratchet wheel in the process of driving shift.
The fracture of the pawl is in the middle of the step near the pawl rocker arm. The fracture surface is rough and
there is no obvious plastic deformation observed. The sintered neck at the broken part of the pawl is not fully
formed. The pores near the fracture surface of the pawl are larger than the normal part，and unevenly distributed.
There are even connected pores in the local area. The microstructure is mainly tempered martensite，plus copper
and nickel riched phases，separately. Hardness varies in different regions. The main reasons lead to the fracture of
the pawl are discussed and improvement measures are provided，warm compacting should be carried out at 140 ℃
and sintering at 1160 ℃，instead of compacting at room temperature and sintering at 1 140 ℃.
2021, Vol. 31 
