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Detailed chemical abundance distributions for fourteen elements are derivedfor eight high-probability stellar members of the solar metallicity old opencluster M67 with an age of $\sim$4 Gyr. The eight stars consist of four pairs,with each pair occupying a distinct phase of stellar evolution: two G-dwarfs,two turnoff stars, two G-subgiants, and two red clump K-giants. The abundanceanalysis uses near-IR high-resolution spectra ($\lambda$1.5 -- 1.7$\mu$m) fromthe APOGEE survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca,Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for2M08510076+113115 suggest that this star is a solar-twin, exhibiting abundancedifferences relative to the Sun of $\leq$ 0.04 dex for all elements. Chemicalhomogeneity is found within each class of stars ($\sim$0.02 dex), whilesignificant abundance variations ($\sim$0.05 -- 0.20 dex) are found across thedifferent evolutionary phases; the turnoff stars typically have the lowestabundances, while the red clump tend to have the largest. Non-LTE correctionsto the LTE-derived abundances are unlikely to explain the differences. Adetailed comparison of the derived Fe, Mg, Si, and Ca abundances with recentlypublished surface abundances from stellar models that include chemicaldiffusion, provides a good match between the observed and predicted abundancesas a function of stellar mass. Such agreement would indicate the detection ofchemical diffusion processes in the stellar members of M67.

Chemical Abundances of Main-Sequence, Turn-off, Subgiant and red giant Stars from APOGEE spectra I: Signatures of Diffusion in the Open Cluster M67