  We present systematic temperature-quench Monte Carlo simulations on
discrete-strain pseudospin model Hamiltonians to study microstructural
evolutions in 2D ferroelastic transitions with two-component vector order
parameters ($N_{OP}=2$). The zero value pseudospin is the single
high-temperature phase while the low-temperature phase has $N_v$ variants. Thus
the number of nonzero values of pseudospin are triangle-to-centered rectangle
($N_v=3$), square-to-oblique ($N_v=4$) and triangle-to-oblique ($N_v=6$). The
model Hamiltonians contain a transition-specific Landau energy term, a domain
wall cost or Ginzburg term, and power-law anisotropic interaction potential,
induced from a strain compatibility condition. On quenching below a transition
temperature, we find behaviour similar to the previously studied
square-to-rectangle transition ($N_{OP} =1, N_v = 2$), showing that the rich
behaviour found, is generic. Thus we find for two-component order parameters,
that the same Hamiltonian can describe both athermal and isothermal martensite
regimes for different material parameters. The athermal/isothermal/austenite
parameter regimes and temperature-time-transformation diagrams are understood,
as previously, through parametrization of effective-droplet energies. In the
athermal regime, we find rapid conversions below a spinodal like temperature
and austenite-martensite conversion delays above it, as in the experiment. The
delays show early incubation behaviour, and at the transition to austenite the
delay times have Vogel-Fulcher divergences and are insensitive to Hamiltonian
energy scales, suggesting that entropy barriers are dominant.
