Effect of Ni on Microstructure and Mechanical Property of a Co-Ti-V-Based Superalloy
Pengjie Zhou, Xinkang Gao, Dehang Song, Yinbing Liu, Jun Cheng
Abstract
The effect of Ni on microstructure, elemental partition behavior, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:msup> <a:mrow> <a:mi>γ</a:mi> </a:mrow> <a:mrow> <a:mo>′</a:mo> </a:mrow> </a:msup> </a:math> phase solvus temperature, lattice misfit between <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:mi>γ</c:mi> </c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:msup> <e:mrow> <e:mi>γ</e:mi> </e:mrow> <e:mrow> <e:mo>′</e:mo> </e:mrow> </e:msup> </e:math> phases, and mechanical properties of the Co-8Ti-11V-xNi alloys was investigated. The result shows that the lattice misfit in the alloys decreases from 0.74% to 0.61% as the Ni content increases from 0 to 10%, and the average sizes of the cuboidal <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:msup> <g:mrow> <g:mi>γ</g:mi> </g:mrow> <g:mrow> <g:mo>′</g:mo> </g:mrow> </g:msup> </g:math> phase were measured to be 312.10 nm, 112.86 nm, and 141.84 nm for the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni, respectively. Ti, V, and Ni exhibit a slight tendency to partition into the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" id="M5"> <i:msup> <i:mrow> <i:mi>γ</i:mi> </i:mrow> <i:mrow> <i:mo>′</i:mo> </i:mrow> </i:msup> </i:math> phase, while Co shows a slight tendency to partition into the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" id="M6"> <k:mi>γ</k:mi> </k:math> phase. The solvus temperatures of the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" id="M7"> <m:msup> <m:mrow> <m:mi>γ</m:mi> </m:mrow> <m:mrow> <m:mo>′</m:mo> </m:mrow> </m:msup> </m:math> phase were measured to be 1167°C, 1114°C, and 1108°C for the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni alloys, respectively, by using differential scanning calorimetry (DSC). Moreover, the yield strength and ultimate strength of the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni alloys were investigated, and the yield strength and ultimate strength of the 10Ni alloy were highest, at 219 MPa and 240 MPa. After compression at 1000°C, the dislocations cannot effectively shear the <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" id="M8"> <o:msup> <o:mrow> <o:mi>γ</o:mi> </o:mrow> <o:mrow> <o:mo>′</o:mo> </o:mrow> </o:msup> </o:math> phase in the 0Ni and 10Ni alloys, resulting in a relatively high compressive strength of the 0Ni and 10Ni alloys. However, the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" id="M9"> <q:msup> <q:mrow> <q:mi>γ</q:mi> </q:mrow> <q:mrow> <q:mo>′</q:mo> </q:mrow> </q:msup> </q:math> phase of the 5Ni alloy is no longer visible, and its strength is the lowest.