While your “estate” can be the beneficiary of your IRA and your Will thereafter determines the distribution of the retirement funds, this might not be best idea tax-wise. IRAs are very specific and peculiar assets with very specific inheritance rules. If your “estate” is the beneficiary of your IRA, then very “unfavorable” withdrawal rules apply. Instead of the IRA being withdrawn over the life expectancy of the beneficiary (typically younger than the plan owner), the funds must be withdrawn within five years or perhaps over your remaining life expectancy. Yes, this can get rather complicated.
Make sure you consult with competent legal counsel when coordinating the distributions from your Last Will and from your IRA.